Well, with respect, there's one even more important aspect:The thing that drives predictability in old-school D&D is the absence of critical hits
The baseline of hit probability.
If one game is designed so that an "average" foe for a hero of a certain level needs to roll 15+ on the d20 to score a hit, I'd call that a relatively predictable game. (Sure you can roll five 20's in a row, but outliers have no place in a discussion about predictability - unless of course they're not outliers at all) More powerful monsters might then need only 10+ to hit you, while weak monsters must roll a 20 to do so.
If another game is designed so the same foe only needs to roll 5+ on the d20, that makes the game much less predictable.
I guess you could say that the game is just as predictable, only predicting "the hero will fall", but now I'm discussing specifically from the player's viewpoint. The relevant question is "can I trust my defenses to hold for X rounds unless I have significantly worse than average luck?" If yes, we call that game predictable. If no, we don't.
What this boils down to is the following:
How large percentage of my maximum hit points can I expect to lose in a single round, against "reasonable" opposition?
Or, even more to the point: how many rounds can I expect to remain standing?
If this number is 3 or more, that game is relatively predictable. More is of course better, but at 3 you reach the significant milestones where you
1) have time to see where things are going
2) have time to do something about it without it being too late
If you can only expect to withstand one or two rounds of enemy fire, then you and your friends generally don't have time to react. (Obviously every number is very approximate, but just to get the point across).
Sure criticals also reduce predictability, but at least in games where they only occur once every twenty rolls, and/or when damage is only doubled or less, their impact is in the end analysis limited.
Pathfinder 2 is considerably less predictable than any other D&D game, in that a hero's hit points might yo-yo between "lots" and "none" more than once in a single fight. Foes are very likely to score at least one hit each round, and criticals come often and early.
You basically have no predictability at all. Being a defensive Fighter does not mean you can be reasonably certain not to go down in the first round of combat. It all depends on how many enemies that target you, if they score one or three hits each, and whether you suffered more than one critical that round.