What weapons do you think the Abrams proved itself against? The Abrams built it's mainly destroying the Iraqi army(twice). That Army was armed with exactly those weapons.
The extra features were not "slapped in" they have very certain purposes. The troop carrying abilety is only for use in emergencys or very special cases. the mortar was added so the tank can better defend itself against infantry. The Merkava was never built to fight against insurgents, it was built to defeat the Syrian and Egyptian armored forces.