He's still a fantastic player.
The way I see it we have two different teams for the two different types of games we need to play.
The first one is a fast paced, gritty, determined team that defends well and ferociously and breaks on the counter with great pace. That's the one we saw today. It doesn't work all the time though. We don't usually have much possession in these types of games and so we don't need Ibra because it doesn't play to his strengths. So we play Rashford, because that's the type of game he is suited to.
The second is the more common one with Ibrahimovic. These are games against the lesser teams, teams we should be beating and dominate possession, playing in their half with us playing very close to their box. This game suits Ibra more and Rashford less, and so we use Ibra in these situations and Rashford out wide where he can whip crosses in. This should work against most teams but sometimes it doesn't, hence our draws.
Our squad overall can fit the bill for both these types of games, but ideally you want a squad full of players that can fit both these types of games. We can't play the first game all the time because it won't always work and Ibra doesn't suit it. But it's good that we have him because he suits the 2nd type of game very well and he's scored a lot of goals playing that way.