It's been a long time, but IIRC you could still group units in SC1 and bind them to number keys. So maybe only 12 at a time, but you could still navigate multiple groups of 12 with just a few keypresses.
But it still means attack-moving 108 units (aka: 9 groups, all labeled 1, 2, 3, 4, 5, 6, 7, 8, 9) requires 18-actions.
That is: 1 (select group 1), then a, then left click on the attack-area. Then 2 (select group 2), a, left click on attack area. Etc. etc.
That's a difference of 18-apm (Starcraft Brood War) vs 2-apm (Starcraft 2). Furthermore, that "Group 1" in SC2 could have 150-units or 200-units (or 400-zerglings, lol) in it. They pretty much made death-balls have 10% of the APM requirement in SC2 compared to SC:Brood War.
I'm all for making the game easier and more accessible: but the death-ball tactic was a little bit "too obvious" and kind of unfun to watch, compared to the tightly coordinated groups of 12 that SC: Brood War was famous for. The groups were too big, numerical advantage was the biggest advantage in SC 2 IMO.
Nuke and Psi Storm exist in both games, but Plague, Irradiate, Ensnare, Stasis Fields are all AoE effects... as well as AoE damage sources (Tanks, Archons, Valkyries, Devourers, and kinda-sorta Mutalisks).
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Lets put it this way: if you really wanted to, you could just have 12-units per group in SC2. But no one would do that, the APM-advantage of having a big group (and manually splitting in the rare cases where a split is needed) is far superior than using 9 groups to split up 108 units.
And sure, stronger players probably split their death-balls into smaller groupings of maybe 30 units or so (you don't want to just A-move all over the place, a degree of flexibility is useful), and only occassionally merges everyone together into a deathball. (Fast and loose is good: you don't want to dedicate an entire army to a battle, especially if they might lose).
But no one is making groups of ~12 in SC2. Its too small.