The plane is just too good to be at 13.3, it has 6 FOX-3 & 4 FOX-2, it is like two MiG-29SMT or 2 F-16C in one plane.
The SU-30MK2 has the same radar of SU-27SM, the N001VEP:
And the SU-30MKK has the N001VE:
The only difference between the N001VEP and the N001VE is that it offers a slightly better detection range and enhanced capabilities for tracking multiple targets, though they behave similarly in close-range combat.
And the SU-30MKK has the option to use the Chinese variant of the R-77 or the Chinese variant of the AIM-120.
These premiums are capable enough to be minimum at 13.7, it has the big payload, the same radar of SU-27SM and the engines of the SU-27 (Which it doesn’t make it slow or goofy enough to be an exception).
It’s not smart for GAIJIN to base its aircraft placement decisions on win-loss statistics, as it depends on the pilot. As you know, most players are low-level, barely know how to fly piston-engine planes, and buy their way to the top tier. But that doesn’t make a plane bad enough to be in a BR that easily outclasses other planes in the 12.3 to 13.3 range.
The average player and experienced players will find it very easy to take advantage of the low BR it’s in, and I don’t see experienced top-tier players struggling.
As you can see most of the times SU-30MK2/MKK pilots do not really struggle.