Bottom is a terrible actor, but he thinks he is a great actor and can do anything.
Bottom is a terrible actor because he overacts, misses his cues, mangles his lines, and does not listen to the director. When Quince announces the parts, he wants to play all of them.
Bottom has a high opinion of his own acting ability.
That will ask some tears in the true performing of
it. If I do it, let the audience look to their eyes; I will
move storms; I will condole in some measure. (Act 1, Scene 2)
Of the craftsmen, he probably is the most capable, but that is not saying much. He has a tendency to argue with Quince and give suggestions. He even argues with the audience, breaking character and explaining that Thisbe missed a cue.
Despite this, the others love Bottom and genuinely think he’s a good actor.
It is not possible. You have not a man in all Athens
able to discharge Pyramus but he. (Act 4, Scene 2)
As Philostrate points out, the craftsmen’s performance of Pyramus and Thisbe is so bad that it brings tears of laughter to the audience. The wedding party enjoys the play, and that is all that matters. Of course, they are not up for an epilogue!
As goofy as Bottom is, his antics move the action of the play along and do provide a lot of comic relief. Audiences will love to see the craftsmen come on the stage, because they know it will be funny!