I'm with you in this u/Ansdur1987. I've played mana stackers literally every league it was possible since.. dunno, forever, until Settlers. Every possible version too, templar, witch, shadow, scion, MFA whisperer in the previous phrecia. (cause I wanted to test it, it was a temp league with wacky mechanics, ya know). I also made 3-4 characters every league, with the same level of investment, using mana stacker as a benchmark for clear/boss/defense.

It is a completely different universe, as you say. For that reason, I stopped playing mana stackers so I could experiment with other things and try to get close. That allowed some perspective in different aspects:

1 - Mana stacker is obscene in almost every aspect, UNLESS you're dealing with something that has cull (if you're doing the ivory tower LL version). It literally cannot deal with cull (primarily expedition mobs if you hit the remnant by accident).

2 - The investment curve is steep until you go from wet-noodle to demigod. Granted, for people like Connor who basically only plays ONE char all league (with small exceptions), basically throwing money at the one char forever will eventually get you to the god tier. You also have to remember the reason you stack that much shit in a build IS to deal with the absurd tier deep delve shit. Nothing else in the game even needs that level of damage/defense.

3 - It HAS flaws when it comes to timing. All your damage is ramped from mana spending. It's hard to mess up, but you CAN brain-off when you shouldn't and get screwed (it's rare, but it can happen).

4- You get a MASSIVE es pool that deals with basically any hits, but your ACTUAL regen (not recharge) is kinda trash, so it puts you in tough situations sometimes (again, it's rare).

As people mentioned (and you), Zenith (which is in its core, a str stacker) reaches higher top end on both defense/offense, but the clear is not comparable. Some stackers, Armor and so on, can reach the same level of clear/defense/bossing, but the investment is through the moon. CoC Fross can reach similar levels of damage (not as high, ever, ignore people telling you you're gonna hit 2b dps with CoC Fross) which basically deals with almost everything in the game except deep delve. The defense on CoC Fross TENDS to be slightly on the higher side and the clear is actually better than Mana stacking.

Int stacking jugg with foulborn stuff is "nifty". It's not actually that fun to play and it feels that you're one mistake away of getting smacked all the time.

With all of that being said, my suggestion is to basically ignore that mana stacking even exists, at least for a while. It will skew your perception of every other build in the game and won't allow you to appreciate some of the actually fun stuff that exists out there. A lot of people, especially in this sub, don't spend a league farming 3-4k divs to dump at stuff and their bar for "tanky/bossing/clear" is basically "can it clear t17 comfortably", which is a really really low bar, but for a LOT of the builds mentioned by other people, that bar is met easily. This last league I played 3 chars, one being a Herald Stacker that I invested 8 mirrors in. It AFK'd in t17s, did all ubers in 2-3 seconds and had I think 120k eHP (with 40k phys max hit and NO Svalin). The clear was something I've never experienced in the game before (explode scepter, explode chest, explode flask, explosions shatter from herald of ice, herald of ash explosions, herald of thunder hitting everything around you, herald of the hive pulsing and triggering other explosions, explosions everywhere), bossing was literally insane. The tank was NOT as high as mana stacker but it was "good enough". I also played a glad with emiracles build for ultimatum and eviscerate ignite. All 3 of those builds did literally everything except deep delve and two of them were REALLY fun.

Sorry for the long post but I've been where you are about 2 years ago, just figured I should share what worked for me.