It may not be the fastest (usually never is) and may not be the most compatible (because it may not be complete vs hacks in other emulators) but what it does emulate is usually pretty close to perfect & will converge on that at least.
It’s Genesis emulator is a great example of that: about as perfect as non-hardware can get… but definitely not the fastest or most fancy
MAME of course has gone in the same direction, but the project is known for its portability. So it means it has many emulation options to use less cycle accurate methods to run on RaspberryPi for example. From my limited experience, those far older emulators filled with performance-focused shortcuts are the default in MAME. So if you want the most acurate emulation, MAME isn't really it.
The rest of their post is about as accurate too
Just look at the source for most any 3d polygon rendering platform. Take the gaelco stuff or the Midway V platform. The CPU might be well emulated (enough), but the GPU is very frequently only simulated at the highest level. Someone might look at the displaylist generated by the CPU and pick out the vertex format, then they copy-paste a generic triangle rasterizer in its place and try to implement whatever features can be figured out. Attention is only paid to things such as interrupt timing and DMA timing, Fifo timing and so on only to the extent that is blocks operation or crashes the CPU.
This is not to dismiss the incredible work in MAME. It is frequently the first and only source of documentation at all. But parent is correct that it's common for more specialized emulators to go dig up more details and get more things correct than MAME.
Sega Genesis is a poor example; MAME runs the entire commercially released library fine, but some homebrew stuff that seeks to stretch or break the hardware doesn't do well (notably the Titan demos).
On the other hand, MAME's 8-bit Apple II emulation is cycle-accurate and you can raster-split mid-scanline by counting cycles (as some people crazier than me have done). So it really depends on the specific driver.
mametesters.org/view_all_bug_page.php?filter=125692
It plays more games but that’s not the same thing as accurate.
MAMEs emulation is incomplete, that’s why there are bugs.