There’s lots of minor downsides, but the first flight wasn’t even made in the USSR, it was made in post soviet Russia in the late 90’s.
These are noted as to be:
Worse radar than the raptor
Worse service ceiling than the raptor
No super cruise, unlike the raptor
It’s faster; has ever so slightly, longer range, and in my opinion never had the opportunity to really show its capabilities.
Yet again, issue is, this is all theoretical math, because the one time it did fly, the pilot didn’t want to push its limits, and possibly break something that would cause an even larger setback.
Yeah, the Felon is plagued with tons of real world problems and limited production numbers, let alone enough qualified pilots with enough skill to fly it.
It’s a quiet limited amount of knowledge out there that’s readily available, as it was flown once, only one prototype was built, and it never saw combat.
Anyone who believes that either genuinely is doing a Senator Armstrong or has no idea what makes something low observability ot not
Also, as you pointed out, this thing is all external stores. To be stealthy you’d need to run a Gun and a Gun only. If that’s internally fitted, of course