Disclaimer, not a real pilot but I have flown X-plane for many years. So, yes, I am biased. But I do recognize the enormous progress MS has made with their latest sim. The visuals are stunning and the rest got a fairly big upgrade as well. It's hard to not get enthusiastic about it. I don't have the hardware to run it but I definitely want it.
Avionics in the default planes (both products) are not intended to be hyper realistic. Study level plane add ons exist for both X-plane, and all of MS recent simulators. They typically cost more than the base simulator and you can geek out over every little part of the plane's functionality. There's a great ecosystem of add on developers for both simulators that can get you a lot of realism.
That being said, Austin Meyer's primary motivation for building and continuing to build X-plane has always been simulation fidelity whereas MS core customers do include some hardcore users, they are mostly a bit more casual users. However, add-ons exist that do have a some hard core users and they do provide an excellent experience.
In between shipping Vulkan support for the core sim (which landed last year), Austin Meyer actually dedicated an entire release (11.40, 2019) to addressing some long standing edge cases with aerodynamics. There's a great overview of that on Youtube where he explains what he did (https://www.youtube.com/watch?v=v4UfGE-JJY4). He even addresses "that new MS sim" at the end of the presentation.
There's all sorts of subtle behavior that he figured out the mathematics for and built into the sim. I like flying tail draggers in x-plane and the behavior definitely improved. It wasn't bad before (famously) and it got a lot better with that release. That represents the level of attention that goes into the product and it's a reason why lots of people like me continue to enjoy that product. It's also the reason you get more sensible behavior at the edge of the envelope for a lot of planes. Some plane manufacturers actually use plane-maker (which is included with x-plane) to model their new models: it's the easiest way to get a feel for how their plane will behave before they build it.
Likewise, the reason the default G1000 is so nice in X-plane is that they have a German contractor who is a real life IFR pilot obsessing about it for years for the past decade or so. His mission in life is to make this thing as real as it gets. And it's apparently very good. I've not actually touched the real thing ever of course but the simulated one is quite a complex thing to figure out. X-plane also has had ways to interface with real Garmin equipment for many years. But that's just one vendor and of course there are many. Most of the other ones are only available via add-ons.
The recent MS simulator does represent a very huge upgrade in realism with better default planes, improved approach to aerodynamics, weather, etc. It's much more engaging without investing a lot in add ons (which in the past was the only way to not make it look hopelessly outdated). Those add-ons still exist of course. Including scenery add ons, airport add ons, etc. It's good out of the box but not that good that those add-ons are no longer needed. In a way it caught up to X-plane's rendering capabilities (and a bit beyond). Where before x-plane just looked way better out of the box. I use a lot of ortho4xp scenery with osm2xplane objects and a few other goodies (all free btw) and you get quite far with just those two. But what MS did is definitely a few levels better. But for a six year old product, it's not bad.
X-plane 11 is coming to the end of its cycle. I expect v12 betas to start showing up end of this year or early next year. I expect that there will be a lot of progress on the scenery front particularly now that they have the Vulkan upgrade out of the way. They've always been good at making the most of data driven scenery production given that they have a small team. And there is a lot of open data to work with.
Avionics in the default planes (both products) are not intended to be hyper realistic. Study level plane add ons exist for both X-plane, and all of MS recent simulators. They typically cost more than the base simulator and you can geek out over every little part of the plane's functionality. There's a great ecosystem of add on developers for both simulators that can get you a lot of realism.
That being said, Austin Meyer's primary motivation for building and continuing to build X-plane has always been simulation fidelity whereas MS core customers do include some hardcore users, they are mostly a bit more casual users. However, add-ons exist that do have a some hard core users and they do provide an excellent experience.
In between shipping Vulkan support for the core sim (which landed last year), Austin Meyer actually dedicated an entire release (11.40, 2019) to addressing some long standing edge cases with aerodynamics. There's a great overview of that on Youtube where he explains what he did (https://www.youtube.com/watch?v=v4UfGE-JJY4). He even addresses "that new MS sim" at the end of the presentation.
There's all sorts of subtle behavior that he figured out the mathematics for and built into the sim. I like flying tail draggers in x-plane and the behavior definitely improved. It wasn't bad before (famously) and it got a lot better with that release. That represents the level of attention that goes into the product and it's a reason why lots of people like me continue to enjoy that product. It's also the reason you get more sensible behavior at the edge of the envelope for a lot of planes. Some plane manufacturers actually use plane-maker (which is included with x-plane) to model their new models: it's the easiest way to get a feel for how their plane will behave before they build it.
Likewise, the reason the default G1000 is so nice in X-plane is that they have a German contractor who is a real life IFR pilot obsessing about it for years for the past decade or so. His mission in life is to make this thing as real as it gets. And it's apparently very good. I've not actually touched the real thing ever of course but the simulated one is quite a complex thing to figure out. X-plane also has had ways to interface with real Garmin equipment for many years. But that's just one vendor and of course there are many. Most of the other ones are only available via add-ons.
The recent MS simulator does represent a very huge upgrade in realism with better default planes, improved approach to aerodynamics, weather, etc. It's much more engaging without investing a lot in add ons (which in the past was the only way to not make it look hopelessly outdated). Those add-ons still exist of course. Including scenery add ons, airport add ons, etc. It's good out of the box but not that good that those add-ons are no longer needed. In a way it caught up to X-plane's rendering capabilities (and a bit beyond). Where before x-plane just looked way better out of the box. I use a lot of ortho4xp scenery with osm2xplane objects and a few other goodies (all free btw) and you get quite far with just those two. But what MS did is definitely a few levels better. But for a six year old product, it's not bad.
X-plane 11 is coming to the end of its cycle. I expect v12 betas to start showing up end of this year or early next year. I expect that there will be a lot of progress on the scenery front particularly now that they have the Vulkan upgrade out of the way. They've always been good at making the most of data driven scenery production given that they have a small team. And there is a lot of open data to work with.