5kilos of weight is nowhere NEAR 2 tenths. Probably less than a tenth. You have to remember that that 5kg will only be a benefit to center of gravity this year; with no weight distribution benefit.
I’ll give that the cars are probably more designed around Seb’s feedback – not that they would build a car that makes Mark slower; but rather their main focus would be centering car design around Seb; and if that also helps Mark; great. Having said that I don’t buy that that would hamper Mark at all. We’ve heard loads of times about Seb taking Mark’s setup data and using that when he can’t find a good balance. We’ve also heard about Mark taking Seb’s setup data and using that when he can’t find a good balance.
Yes they may have different driving styles; but different styles could also require the same things from a car; and judging by the way they share setups so closely; you would have the same needs from a car.
To answer the thread question; should he retire of his own volition? No. What on earth for? He’s probably got the best chance of winning a race where he is right now. “Should Red Bull retain him,” however, is a different matter.