Firstly, Ilya's a good-for nothing besides being a prana provider for Berserker.
Ilya pretty much did the same thing Gil did, lots of power, but didn't use it, could probably kill Rin in a serious 1 on 1 (course, works both ways, Rin could also kill Ilya).
fact remains that Ilya = homunculi (even the real shitty ones > the average magus), and Ilya = has a very very powerful magic crest which stems from a very very powerful family.
What I'm saying is, Berserker is a strong Servant, no doubt. But that's as far as he goes, if he's still a Berserker.
I'm assuming you're talking about the heroic spirit, rather than the class in general.
Had Saber(King Arthur) been summoned as the Beserker class, and Beserker(Herc) been summoned as Saber, i assure you, Saber(King Arthur) would loose.
course, that would depend on how insane Saber was...aka, sane nuff to use Excalibur or not.
this is of course ignoring the effect of masters (shitty master vs good master...etc)
tbh, the fact that Herc still remained so powerful/threatening after being Beserkerized is testament to how powerful he really is.
Beserker class has some definite weaknesses, and only a few heroic spirits (i would imagine) would have NP's that compliment the many restrictions batshit insanity imposes.
I order the club sandwich all the time, but I'm not even a member. Man, I don't know how I get away with it.