AMD would have been good and well if they hadn't bought ATi and overpaid for it.
I don't think buying ATI was the problem, it was not capitalising on that investment for a long time. GPUs kept the company afloat when the CPUs were in limbo. All that crypto-mining probably paid for the various Zens.
It's also given AMD a unique portfolio of IP that consists of both CPU and GPU IP, that they've used to leverage against each other quite nicely.
The biggest problem AMD had around the time of buying ATI and afterwards is probably divesting from GloFlo, but being tied to them for years, and having people at the top who didn't seem to have Lisa Su's long term vision and technical background when it came to where the company was going to go.
AMD without ATI would just be stuck in the doldrums, getting crumbs from Intel's table, with likely not much to offer but second league CPUs.