I play a lot of Dungeons & Dragons Online, a fairly old MMO with a fairly old engine but they still keep producing content. There used to be a Mac client but that broke a long time ago and they don't have the resources to maintain it. So currently you have to play it via the Windows client but, although this is a third-person virtual environment not-quite-shooter, the graphics requirements are not that high.

I usually run this with CrossOver, which is based on WINE, on my Mac. This is mainly Windows API translations to Mac APIs. The Windows app thinks it's running on Windows and as long as it uses the normal APIs it works fairly well. A lot of programs require installing .NET framework or various other libraries into the CrossOver bottle (a bottle being an environment so you can have each app run in a bottle custom configured for it) and getting any specific app working on WINE is a pain as you install dependencies and stuff and that's what CrossOver tries to ease by having app-specific scripts to configure a bottle correctly.

Anyway, it's not running Windows and it's fairly efficient. I can run DDO (at lower graphic settings) and it runs fine most of the time with some weird hiccups like when you stop running (take your finger off of the run key) you keep moving for a second or if you're in mouse look mode and go to another Mac app to do stuff when you get back to DDO it kind of goes haywire for a bit like your mouse is drunk.

And I can run two DDO clients to run two characters. Switching back and forth there is a second or two lag and if the DDO windows overlap they both might think the mouse is active in them. There is a utility for this use case where the utility can be set so that one DDO character auto-follows another and it's pretty good at it. But so far I haven't gotten the utility to run in CrossOver with DDO -- maybe it launches into a separate space so doesn't see the DDO window appear (normally when it sees that window it'll add an overlay toolbar).

I experimented with VMWare Fusion running Windows 10. Fusion is a virtual environment that maps PC hardware to Mac equivalent or virtual hardware. Windows thinks it's on a PC with an Intel chip and it runs normally. Theoretically the virtualization is not that much of an overhead with newer Intel chips since they support virtualization better. But on my MBP (last version that used Intel) it's definitely a bit slow. Kind of usable running an app or watching a video but I wouldn't want to run the latest Windows games on it.

I use Steam and DDO. DDO runs ok though mouse tracking is very off (Windows it's fine then click into DDO and either too fast or slow). I can run the DDO util and do auto-follow and that works fairly well (so I run on DDO client in CrossOver and the second on Fusion). But if I have to do anything complex with the Fusion DDO client (like actually fight) then it's kind of too slow to be usable (though doable if I wasn't running a second DDO and nothing else on my Mac).

In summary, from my experience, if the Windows game runs in CrossOver then it's a far more performant experience than trying to run a game on Fusion. Desktop apps like a word processor or spreadsheet are probably fine and maybe better on Fusion with real Windows and the various extras you get that way. But Windows games I'd stick with CrossOver and give up if I need Fusion.