I honestly feel like people exaggerate SM Ash's personality. He's really not all that different to XY Ash, Still good at battling, still a caring person who is willing to help out his friends and encourage them. The only real change I've seen is that he's more hyperactive and often gets himself hurt for comedy purposes but the second part is just the fact the writers are playing up slapstick more than other series rather than Ash doing anything overly stupid.
Amour would still work fine with Alola Ash. Thus far the only "dumb" thing I feel he's done is when he jumped to try and grab the Milotic Lillie reeled in which was still done with noble intentions even if I have no idea what he was planning to acomplish, Other than that he hasn't done anything dumb, or acted stupid like people claim. Serena would probably just giggle at Ash acting all hyper and he'd be the same caring guy he was to her in XY
I don't think you're watching the episodes for SM thoroughly enough. There's more of these moments than that scene.
From the top of my head there's:
- Ash jumping in to help Lillie reel in the Milotic only to get hit by it (the one you mentioned).
- Ash carelessly touching the tail of an Alolan Exceggutor only to be hit by it.
- Jumping into a field of Tauros and getting run over by them.
- Putting too much detergent into the washing machine causing it to overflow.
- Putting too much ingredients when he was cooking.
- Running into the shopping mall doors 3 times.
That being said, there are some good moments to it like the Z-move scene, the Litten episode, the Rowlett episode and the Lillie episode (points for AmourShipping reference too).
Regardless of the case, Serena will always like Ash no matter who he is. It doesn't even look like that she'll hate him either except when he's not himself. If she was in SM, she'll probably joke around with him too or facepalm at his idiotic moments... with love.