X-Com 1 and 2 (new versions) are great games, even if they moved away from the large squad slaughter that was Enemy Unknown, terror from the deep and partially Apocalypse. I personally really enjoyed looking at black sections of the map and thinking "that will cost 3 rookies to explore"
Everyone is aware of the "95% to hit meme" around X-Com, and if you've played Phoenix Point, the difference is especially jarring. If you haven't, aiming in that game is purely a probability cone, so standing point blank next to an alien means something. In X-Com it doesn't mean diddly squat.
I finally figured out what the problem with X-Com is, and why it's always uniquely frustrating. With it's pod based mechanics, fake stealth and drip fed enemies. What you are seeing on screen has no relevance and only serves as a distraction. Being right next to an Alien and missing is irrelevant because where the character and alien are on screen do not correlate with the game.
X-Com is, for all intents and purposes a very fun card battle game. If it were a Dos prompt game, with exactly 0 visuals, nothing would be lost.
Try it next time you play, completely ignore the visuals and imagine your character as a card drawing a dice based attack against another card.
Templar will carry you hard for the first half the game between their guaranteed hit melee and their one ability to deflect any one shot at them after a kill. By the time they fall off, you have your other units ready to get the slack.
Considering the early game is the hardest part by far, I'd lean towards Templar being the most powerful in general terms as they provide something concrete at a time when no one else can reliably do so.
Reapers are capable of doing some wild shit and cheesing the fuck out of the game, but by the time they can do so you probably have many options at your disposal. And they rely heavily on the, as you said, broken Stealth system unless you mod it.