Take a card game like Hearthstone or poker, a skilled player can calculate the probabilities of drawing a card so while luck/RNG plays a huge role, the player can play around it since it is consistent
Really, you're going to give Hearthstone as an example of consistent RNG? A card game which literally everyone who has ever played another card game agrees is one the worst if not THE worst possible example of the genre in that regard?
(Honorable mention is tank phasing since sometimes tanks block each other while other times tanks go through one another.
Tank phasing is nearly completely binary. Both vehicles moving, you phase through. Only one moving, you can't phase through (not strictly true, but it's so unreliable you could be spamming move commands for 30+ seconds before you phase). All that you need for the phase through to happen when both are moving is to spam movement commands, within a second your vehicle will start phasing through the other one. Very honorable mention.
Sometimes a 50% hp squad will have full models. Sometimes a 30% hp squad will have full models. I've even seen less than 5% hp squads have full models. There is absolutely nothing the player can do to influence whether a model drops.
The CoH2 infantry health bar is just an UI nicety, rather than cluttering the view with individual health bars for every member it combines them all to a single bar. Not like you have control of individual entities anyway so there's no need for you to know their health. I sure as hell wouldn't want some convoluted system where the squad health is its own little thing and where at set milestones it'll kill off members of the squad. Not that there is any chance whatsoever of such a major rework anyway.
AOE weapons leaving lots of low health entities alive is just the way things work, nothing random about it (apart from where it lands and thus how many entities it actually affects). Deal with it.
Small arms targeting would be the "random" part in the equation. Every accuracy based gun will pick an individual target from a squad to fire at, and won't change that target until it dies or it can't be fired upon anymore for some other reason. Targeting entities inside a squad seems to be random when there are multiple targets at roughly the same range available, but maybe there is some inner game logic to it that we just don't know.
If you're running around with a grenadier squad and run into an enemy squad at max vision range, then the guy that is going to get targeted from the grenadier squad will be the one in front of the "diamond" formation. No randomness, because he's the first viable target to enter the range of all enemy units, so they all focus fire on him first.
So understanding this, if you think your squad is targeting the totally wrong entity in an enemy squad, give them a move order backwards and thus force them to abandon their current targets, then immediately a-move towards the enemy again. In some situations you might actually get your squad members to target what you want.
Overall I'd say giving players the opportunity to target entities within squads would just lead to way more cancer than it would ever add to gameplay depth, so I'd be against that sort of change. Not like it would happen at this point in the development cycle.
simple RNG problems that are still in the game such as vehicle abandons, weapon drops
Actually right about these.
and mine crits.
The minor chances for engine destroyed have already been removed months ago, there's almost zero RNG to mines (or grenades), the only thing you need to work out their exact effect is the formation of units that are about to trigger them.