Attacking well with a hundred unit stack still means evaluating the enemy stack and figuring out which units should attack in which sequence. That's tedious.
Yes. 1UPT is always tedious, and MUPT is tedious when attacking, but not necessarily when moving.
Optimal CivBE play means getting up the upgrades and bringing the precise amount of units to bear as will be effective. More is not better. That is precisely the sort of MUPT thinking that probably gets too many people in trouble, and then they blame the system, not their own mistakes.
If you can't use more, you're just not thinking far enough ahead. If you have more units than you need for target X ... attack more targets. Win faster.
You can fight an extended front, but I really don't see the point of engaging enemy units in non-city locations. If you have more than that, most of the excess will simply mill about and complicate positioning as they take up positions other units should be occupying.
There is more than one city most of the time. Usually a lot more.
I find the position game more entertaining.
The idea that positioning doesn't matter with MUPT is false. Positioning is actually much more complex in MUPT. Then you have the choice of whether or not to stack.
Stacking was rarely optimal. And even in circumstances that lead to stacking being optimal, it was sub-optimal choices that lead to those circumstances. Yet you still ended up stacking to some extent to take advantage of roads and passing through chokepoints, or in specific situations when unit composition called for it. Those situations had risks involved in all but Civ III, because stacking lead to increased damage taken.
That's interesting.
"Ranged in the back ... pew pew pew" is not really deep or interesting. ~100% kill rates vs a completely outmatched AI gets boring quickly. That's essentially what 1UPT in Civ has boiled down to.
What you are actually addressing in your remarks about MUPT is laziness and incompetence. The AI is incompetent, and so needed stacking just to get it's forces into action. That at least allowed it to bring it's bonuses which it relies on for difficulty to bear militarily, even if they still wouldn't be optimally positioned. Stacking was necessary to allow the AI to compete militarily. They could have more units than the player because of bonuses ... a numbers advantage they sorely needed to give any sort of resistance. Because with 1UPT, you build 10 units and you're invincible. Doesn't matter if the AI can build 10 or 100 to throw against you ... they're still never going to threaten a competent player because only 10 of them at a time can make it there.
Players could also play the SOD game, but by doing so they were simply playing down to the AI's level. Players who knew how to play the game rarely relied on SODs ... early rushes, chokes, keeping the FOW back, and misdirection are generally superior uses of units to building up a SOD. But being able to stack was still very helpful in reducing senseless clicking.
For instance, with MUPT, I can produce a unit in an interior city and with one click send it 20 tiles to near the front. It will get there ASAP. With 1UPT, that won't work. Other units moving around will screw up the pathing. So if you want to get the unit to the front ASAP, you have to manually move it (and every other unit) each turn. The in-game pathing is useless.