Honourable Mastan Khan,
You have correctly pointed out that fighters such as Su-30 Mk1 (max loaded weight 85,600lbs capable of carrying 12 missiles and F-15 ( max take of weight 65,00 lbs) that carries 11 missiles, need 2 engines to have the world beating performance. Your point however reinforces my earlier post that since US has no engine with 129.8 kN dry thrust, two P&W F100-220 engines with 64.9 kN dry thrust each power the F-15.
My argument is that apart from redundancy, having 2 engines do not necessarily mean more capable fighter. Should a reliable and powerful engine such as Pratt & Whitney F-135 (125 kN dry & 191kN with reheat) that is fitted to F-35 be available, you don’t really need 2 engines; depending of course on size & weight of the fighter.
I stand by my assertion that as long as technology level is the same; I would prefer a larger single engine to 2 smaller engines because 2 engines would weigh more, cost more and require twice as much maintenance. I would only go for the two engines for the lack of an alternative.