There are 2 major reasons the 1 dps + 3 zdps meta exists. Scaling mob dmg requires as many buffs/cc you can get to keep the dps alive at higher Gr lvls. The second and really the bigger issue that will prevent even 2 dps is the lag. D3s servers simply cant handle the numbers. This is why zdps go with no area dmg or LoH. In its current state, the game would lock up every time you grouped up enough mobs to kill with 2 dps .
For most of the past seasons 2 dps + 2 zdps was the meta because it provided the best utility combined with the best dps and the least lag. We saw 3 zdps start in S3 speed runs only because people wanted to leach XP+gear on their dps class but it was uncommon, in S4 supports were able to act as dpsers thanks to Static Charge monk proc'ing from everybody's attacks but there was still many groups with EP monk + SC monk. S5 is when 1 dps + 3 zdps was mandatory and it has nothing to do with buffs or lag, it was entirely because of a brokenly OP sword and a brokenly OP passive that allowed 1 class to pump out lingering AoE spells that scaled exponentially and reached heights unforeseen by the devs.
Lag is a byproduct of too many mobs taking damage too frequently. The game was designed around the assumption that mobs would die fast so things like DoT's ticking many times per second or the Area Damage stat which proc's multiple times off of spells that already do AoE damage (aka exponential scaling) are okay when things die fast but it lags to all hell when you group a ton of shit together and it never dies. They have slowly been redesigning things ever since S1 to reduce the number of calculations but AD is fundamentally flawed, DoT's need to tick less frequently, and mobs need to leash to prevent over-grouping (too much density).
The meta is controllable, they can promote builds that cause less lag by making those builds' dps the highest, they can reduce the utility of support specs, they can make DoT's tick less often, and they could redesign AD to only work with single target spells or only proc off the first target hit ortons of other things that don't create exponential calculations...