This race was a toss-up. He lost by a few points, and I do not think one can rightfully say he didn't have a chance in that case.
At most I think one could say that the fundamentals of this district gave Republicans the advantage, but recent events definitely made it viable. Being competitive/a toss-up doesn't guarantee Ossoff will win, it just means he had a shot.
Being anti-Trump and nothing else isn't an election winner.
Was he? It is my understanding that he went out of his way to avoid basing his campaign only on Trump bashing. I get that the national party is all in for anti-Trump stuff, but that doesn't mean Ossoff was.
Plus, let's not forget that it is Trump who made this district competitive in the first place. Issues like healthcare will help, but it isn't
the reason.