Re:AWS, this test benchmarked Cloudways managed WordPress on top of AWS. They don't specify instance type, underlying software config, etc. This has little to do with AWS.

CloudWays told me they deployed the same stack on AWS/Digital Ocean. I do specify what instance type (m1.small 1.7GB instance) vs 2GB DO droplet.

We do a lot of AWS work, so it is interesting to see the poor AWS performance. Any theories as to why it might be?

I think AWS is best suited for companies really using many of the services in conjunction with one another. If you're just after raw CPU/RAM/IO, I think EC2 is overpriced as an option. Guys like Digital Ocean are offering a lot more bang for your buck (as the testing shows) on that front. Digital Ocean also lacks a ton of the features of AWS, so that's the trade off.