Flourishes wouldn't be OP, as the 1st strike has roughly the same cooldown as the 3rd strike, and the 2nd strike has the shortest cooldown
Cutters would be useful because they have fast attack cooldowns
Difficulty increased due to having less opportunities to attack without getting hit
Less gun & sword chargespam as it's more dangerous
Bombs are more useful as they're a safer option
LD balance(strikers and alchemers are less spammy) >> better framerates
SK becomes less of a trigger finger/input spam game
The game wouldn't necessarily become more casual, but actions will be more tactical, thought out, and slower paced.
I played T1/2 without a shield to get a feel for using weapons without shield-cancelling(I habitually shield-cancel as many animations as I can, so it's easier to just play T1/2 without a shield instead of trying not to shield-cancel in T3).
Of course if there wasn't shield-cancelling, weapons like Winmillion and Troika would need some sort of boost as they'd be extra-disadvantaged by this change(mediocre damage and long animation times).
I'm not advocating for the complete removal of shield-cancelling, just hypotheticals.
SK becomes less of a trigger finger/input spam game
This is entirely wrong. Without shield cancelling, the game would (at least for swords) largely just be about being able to interrupt/knockback as much as possible because there'd be no other good ways of dodging for most swords. Currently, swordsmanship is a lot about technique and timing. Without shield cancelling, several techniques would be impossible to use and timing would become less relevant. In the end, I don't think this would make swordsmanship anything but a matter of clicking as fast as possible.