F-117 has great stealth but poor speed and flight performance.
The engine blocker limmited F-117's speed, F-117 is a sub sonic bomber.
You russians ####ed up T-50's design and now you try to go back fixing it. You russians realize that to completely redesign T-50 will cost way too much since your and your indians friend dont have much money like China does. Therefore you russians came up with some idea using engine blockeer.
If you russians do use this. Then T-50's speed will be limmited, so your stealth gets better but supercruise gets ####ed!
Also, T-50 lacks the great craftsmanship of J-20, with billions and billions of riviets! Which means even with engine blocker, T-50's stealth is still crappy