Yeah, but as you say, MXNet doesn't have the market of PyTorch or TF, and while AWS has deep ties within MXNet, they don't outright control it to the same extent that Google owns TF or Facebook has PyTorch.
It's an Apache project sure, but AWS employs the vast majority of contributors. I'd say in practice it controls MXNet like G/FB control TF/PT. Although MXNet is a much more community friendly project than TF.