> It really influences in performance? when i see this message i think of some
> graphical glitches, but performance issues?
You're absolutely right, actually. There are known graphical issues in a bunch of Namco System 22 games. The specifically known graphical issues are documented here in the source code: https://github.com/mamedev/mame/blob/master/src/mame/video/namcos22.cpp
It's not terribly user-friendly to have those issues only listed in some source file that only a developer would see, but the amount of effort that it would take to provide a comprehensive list of graphical issues on a per-driver basis would be massive, and it would stand a good chance of being wrong or outdated pretty quickly.
The people taking the piss out of you aren't MAME devs themselves, so please take what they say with a grain of salt. The reality is that Namco System 22 is actually a pretty beefy driver. I'm glancing at the source code here, and in addition to a 25MHz 68EC020, it's got two TMS32025 DSPs running at 49MHz apiece, and then finally a microcontroller at about 16MHz for I/O.
Speaking for myself, I've got a pretty capable machine myself - an i7-5930K at 3.5GHz - and I have trouble running PC drivers in MAME, and in terms of emulated processors we're just talking about a 33MHz 486. So I could totally believe that at times when all of the emulated CPUs are running flat-out, even a pretty modern system like yours or mine might not be able to handle it.
That's an interesting observation that your CPU load is only peaking at 50-75%, though. On one hand that could be due to diminishing returns on multithreading: All the CPUs are run on one thread, because they have to be. The technical explanation is kind of lengthy so I won't get into it, but I'll happily go into details if you'd like. The only thing that gets threaded off is the software rasterization of the polygons themselves, and there's only so much that that can do when you're talking about a combined 150-ish MHz being slung around. Just to be on the safe side, try running with -numprocessors 4, and playing around with that value, and see if your performance improves, or if that number changes.
Other than that, it's pretty safe to say that System 22 is just plain a demanding driver. The one (AFAIK) other emulator from back in the day, Viva Nonno, pretty much just shunts around all of the graphics DSPs and tries to implement equivalent functionality using bespoke code, something which isn't really applicable to a project that tries to be accurate when possible. Sorry that the answer isn't a more positive one, but I hope that this at least clarifies the situation a bit better for you.