The Bison wouldn’t be a 13.0 aircraft in my opinion and most likely 12.7 and simply due to the lack of missiles It would carry.
And you need to remember that most 12.7 and 13.0 aircraft get sucked down to 12.0 pretty frequently and the current major issue you’re concerned about is decompression not the vehicle receiving R-77s itself.
I’ve mentioned this many times and will mention it again, the Bison equipped with R-77s would have a similar performance to the IRIAF F-14A.
Both would have ARH but the Fakour-90s would be overall far superior and the host aircraft in general would have a larger kill potential due to significantly more missiles on board like the R-27R1s and AIM-9Ps.