Of course, there are other ways of making opponents skip turns, from slipping on ice surfaces (then again, that's obviously a major part of ice sorcerer, aside from raw damage) to confusion, hold person, and disarming. The latter conditions however are ones that opponents can make saving throws against, allowing them to return from the incapacitating state.
It's literally no different to most offensive abilities requiring Attack Rolls (Or Saving Throws!)
Both Saving Throws and Attack Rolls require your opponent to fail a roll for them to apply (Sometimes there are conditions for still having half impact on a successful save... Though a failed Attack Roll is always 0 damage)
Controlling enemies can in fact lead to more damage than raw damage output. Like in the case of Hold Person, I could cast 1 leveled spell worth of damage... Or I lock an enemy down and make the other 3 people on my party have at least 1 turn of dealing double damage with free attack rolls...
I am aware of the power of both of these; on the higher difficulties, I'm already making my wizard Abjuration, rather than Evocation. The problem I've found is that Arcane Ward is fairly weak on lower levels, because it's quickly depleted - and at least on my first attempt, Abjuration spells that are reactions, like Shield, didn't actually build up any Arcane Ward. I have no doubt it's going to come online later. But that's kind of the problem with a lot of powerful builds.
It can come online pretty early actually. Around level 5.
1 level dip into Fighter for Heavy Armour Proficiency, then take Heavy Armour Mastery as your level 4 Feat and Warding Bond from a Cleric (It's a Level 2 spell so accessed very early). Then so long as you've gone around collecting a bunch of random magical items that are strewn over Act 1, you can stack Arcane Ward pretty easily.
It'll hit its power spike when you get to Grymforge and thus can access the first Heavy Armour with innate damage reduction on it (The Adamantine Plate), but the build overall comes online as soon as you get the Feat and Warding Bond together.
A Monk in the party as a support damage dealer, like hireling Sina'zith, is fun to me - a Monk Tav however has little to no skill points left for Charisma, and that was the reason I brought up Dex, Con, and Wis. Especially on Honour Mode, I would still like the option to talk myself out of as many dangerous encounters as possible.
I don't find it particularly difficult to afford reasonable CHR points when dumping stats, even on Honour Mode.
Like, yes, pump WIS as high as possible... But then like 14 Dex, 14 Con, and some points into CHR isn't too hard (Plus Proficiency from Background and/or Rogue dip (Which you'd want for Fast Hands anyway)) which does enough.
I don't find the need to pump Dex and Con to the moon even on Honour Mode. Especially with proper control available through a decent Tank and control spells.
So as you can see, it's not just that Ice Sorcerer is one of the strongest builds - it's that the builds it synergises with are also some of the strongest builds for the other classes. 
The thing to remember is that those aren't necessarily the strongest builds for those classes. Plus those builds can synergize with other strategies too.
Like, Tempest Cleric with the Spark set up pushing enemies into a corner can still be amazing with Fire buidls, stacking Walls of Fire onto them. Sure, Wall of Fire doesn't benefit from Wet, but it just does a bunch of raw damage on its own.
Light Cleric is ironically more defensive than Tempest Cleric, thanks to Warding Flare.
Debatable. Light Cleric gets Radiance of the Dawn, Scorching Ray, Fireball and Wall of Fire. Potent Spellcasting can also be used alongside Spell Sniper: Eldritch Blast for nice damage too. These can allow the subclass to deal a bunch of damage.
I do want to try out what it looks like when I build my entire team around fire damage (Fire Sorcerer, Light Cleric etc.). But I assume that's quickly going to devolve into barrelmancy, at least when it comes to large enemy groups. Grease alone won't add as much damage as Water does for Cold or Lightning damage.
I've never had any need to "Barrelmancy" to make fire builds good. Wall of Fire is simply so strong on its own for AoE damage. Sometimes I like to combine it with Hunger of Hadar to ensure ranged enemies run into it (And enemies all get slowed) and then things like Repelling Blast and Fighter/Barbarian/Monk/Bard characters that can push enemies back into the killbox if they manage to leave. (Which again, highlights that Raw Damage isn't always the best form of offense... Hunger of Hadar as a control tool can facilitate so much damage in such setups because of how it makes enemies get stuck inside massive damage areas)
I found Ranger the most disappointing class overall - the main one I hear people gushing about is Gloomstalker, but of course in combination with Assassin Rogue.
Aye, I'm not a big fan of Rangers in this game. Even the Gloomsassin build just feels kind of trash after they nerfed Assassin (It used to be that you'd benefit from Assassinate: Ambush on the attack you initiated combat with, meaning you'd be able to do a guaranteed crit full attack to start combat, then get another guaranteed crit full attack from Assassinate: Initiative and then get your guaranteed crit mainhand attack from Gloomstalker. But now you only get Assassinate: Ambush while in combat so you miss out on that first full attack crit)
Even more so given all the "Combat after forced dialogue" or "Forced combat" encounters in the game that can just completely remove Assassin's bonuses completely.
Beastmaster could be decent... If the companions stats weren't absolute trash on Tactician... The bonus damage and effects (Along with Hunter's Mark synergy) could be useful, but on Tactician the companions all have like 40% accuracy and die if anything sneezes near them...
Meanwhile Hunter is just bad... Like, outside Colossus Slayer + Arrow of Many Targets it's just an inferior Rogue/Bard (And the level 11 skills are just awful. Arrow of Many Targets is far better than either of them)
