Schliemann cut that huge trench into the citadel mound at Hissarlik, but had a good reason (for him) to do that, and that inhibited a better understanding of its history. Evans' first find of tablets at Knossos might have contributed a great deal to modern understanding of a vanished civ, but he ordered them laid out on a nearby hillside. A rain came in the night, and, oops, no more tablets. That was just due to stupidity.
Even after accumulating a large number of tablets, Evans refused to publish any but a handful of inscriptions, insisting until his death that there was no Greek recorded in them, and also holding on in hopes of deciphering them himself. That was due to venality. Oddly enough, he came across a word that appeared to be Greek, made mention of it, and then rejected the reading. Ventris cracked Linear B in 1952, and it is Greek. Linear A has been shown to be something other than Greek, although what that something is not agreed on. :')
Both of them obviously made enormous contributions in spite of their failings. By attempting more, they had more serious failures. And had they not made their attempts, as you said, perhaps nothing else would ever have been done.
It seems one of the hallmarks of many successful people is the tremendous failures they experienced..
They did not let those failures discourage them from trying ( and failing ) again however, and through determination, finally acheived their success..