Yes CPS2 games are undeclocked by default (74% IIRC) by mamedev's choice but that's far from always being ideal.
Anyway, no matter how you present it, it's silly to hardcode that. The slider is the best solution to search and do many fine-adjustments.
Anyone can do it.
The only reason people are not using the saving CPU slider is that they ignore it exists, or are inept enough that they don't know how to turn 'cheats' on in the mame.ini
OR because as I've said so many times here and there but it's ignored by mamedev and Calamity & Co., the problem is the CPU% slider's full granularity not appearing in the UI (no decimals) which leaves the user blind for fine-tuning and forced to check and edit the .cfg's
Cools suggested it would be even better to directly show the Hz there instead of a %, in which he's probably right but that might not be easy to do, while showing just the decimals might be a simpler and quicker modification.
As per usual, I'll basically have to be the token a-hole wrestling devs in the mud for a year or two until one hears me over the "Im a victim dev slaving for evil ungrateful users" song that blasts in his head every time a user points an issue or requests something even worth consideration, and actually fixes that absurdity (the one who originally created the UI clearly made some odd choices btw, too bad he just abandoned it there)
I think haynor666 demonstrates it well there, it's the same story as with vsync_offset and the specific.ini's overlapping bug before, or even nvidia prescaling bug waaaaay before (Ive mentioned that one to mamedevs many times in like 15 years and it just got fixed); people are either so inept when it comes to using software - or way too skilled like the real nerds who dont use the UI nor inis and therefore dont experience the same problems as the plebs - that until the matter of useability is fully attended, an emulator's (or whatever other software) features have no chances to be noticed/understood/used by them, only the more or less power-users little demographics will know and that's how things stays stuck in the niche.
RetroArch is crap, but almost everything, including the incredible shaders settings (the only good reason to use RA), is controlled through the UI and the settings actually save.
When you ask something like that to mamedevs there's an absolute psychopath that pops up telling you to hang yourself and like finish dying with your entire family in a fire. I'm not even exaggerating.