How can compatibility not have to do with bloat? Entire subsystems in Windows are devoted to backwards compatibility. If you follow Raymond Chen’s blog on MSDN, he talks all of the time about all of the hacks in Windows to make it compatible with one specific program.
There is still a 32 bit version of Windows in 2018.
There are a few hacks here and there that, I assume, introduce a bit of overhead, but the real problem with 10 is the absolute disregard the Windows team has for performance.
Windows 7 has the same level of compatilibity (or perhaps even more, as I'm sure more software is compatible with it) but it's much lighter.
There is still a 32 bit version of Windows in 2018.