Blood Lust is actually a really good item! Half the bosses in the game are Minionmancers, including two of the most significant set bosses(Mom) and it's mildly useful in a lot of regular rooms because it charges up in about 4 kills and you can see up to 12 monsters or so in a room.
Samson still sucks though because he commits the cardinal sin of lowering his base damage output for no reason! Attacking more slowly?! Christ! If he had a bit of +Speed or something to help make him unique... you could argue that they want the characters to be good in different ways without being too good, but you end up with Cain and Judas at the top by such an incredible degree it's ridiculous. Maggie and Isaac are good for different reasons, but not great. ??? is the challenge mode, fair enough. But Eve and Samson are just painfully bad.