While a lot of these are highly situational they are still more practical than we think simply because you'll notice they cover a lot of different distances and he even showed ones that work on open walls like Dojo.
So in theory if a Jak player was good enough to know and understand all of these different situations he could potentially get a lot of these to work.
The only problem is all of these only work on grounded opponents in this air camp fest of a game but perhaps Jak can pressure an opponent enough to keep him grounded. And after all it only takes one good read and his backwards down circle (unblockable charged) is shown to have a lot of potential here even for hit confirms.
At first glance logic does dictate they'd be highly unpractical. But that's only if they only work at one specific distance/spot on the stage the opponent will learn to stay away from. But what if there are multiple different distances that can be adapted depending on where one lands the hit confirm like here?
It would take a ridiculous amount of practice for the Jak player to know and understand all these situations AND have the state of mind to apply all of these in a match but it's not impossible. His spacial awareness would have to be top notch. He'd have to understand for instance, when he's on X point on the stage where Y combo will work.
For wall combos I think understanding the rebound distances and amount of knockback per move in this game is highly underrated. They could go a long way.