It was a really stupid move by Fabio, I think best summed up by Aleix when he said that Quartararo has that Yamaha working so well that he can easily fall into overconfidence and try moves he shouldn't.
But while he may have cost Aleix a shot at the race win (and his post-crash pace suggested he was definitely in with a real shot), ultimately Quaratararo paid the biggest price for his cockiness. Had he stayed on and Aleix gone out, then maybe a penalty would be reasonable. It's also not a penalty with any recent precedence, with many other riders making similar mistakes with no consequence beyond some awkward forced apologies in front of a camera. Meanwhile, every weekend sees multiple riders dawdling on the racing line in QP with minimal consequence. At least Miller got hit with a long lap for nearly killing Vinales this week...
I think the current stewards have to go, and be replaced with some folks who both have recent racing experience as well as an ability and willingness to articulate why or why not a penalty was assessed. I'd love to see Sylvain Guintoli in the role, but I can't see him signing up for the inevitable abuse. Like being a ref in any sport, the criticism will always outweigh the praise by a large margin...