Is using Android with GApps as bad as running Windows on your PC?

I'm gonna go with no, because of containerization and permission management. On your computer, any program can do pretty much anything, unless you explicitly take measures against this. On a smartphone, you get a lot of control over your apps. In newer Android versions you can even completely disable cameras and microphones (even if only in software).

I would use a throwaway account and avoid giving Google any personal data tho. Of course they could still figure stuff out, but it's harder and unreliable, not to mention super-duper illegal (at least in the EU), so I kinda doubt they go the extra mile.