Simon isn't unwatchable to watch at all
He has economic strokes and movement indeed.
When he doesn't feel confident, he can play too defensively indeed and generally loses but he can be more aggressive in some occasions with his flat strokes when he wants to, he's capable to change the rhythm and the pace of the ball quickly while staying consistent from the baseline: it's when he plays his best tennis in this case.
Also, in his match against Monfils at AO, he was the more aggressive player in the first 2 sets especially on big points and then he got injured in the last 2 sets and fought well to win the match so he deserves respect for that, if Monfils couldn't take advantage of Simon's physical state, it's his fault...
To answer the question, i don't like watching players who hit 100 UES per match, it's disgusting to watch.