I think it was both. A3S had super tight DPS checks that were sometimes down to the button press for my group (though we had one underperforming dps player, so that didn't help), but even when you pulled out the numbers right, individual mechanics could still wipe you at any time.
I think the better way to have worded what I meant is mechanics first, not numbers? It was a lot of DPS check complaints that ultimately stemmed from other pain points, or basically enrage wipes not actually being the norm, just a lot of "we'll enrage at this rate!"
Basically, I just remember a lot of "if only he had less HP!" nerf requests instead of the mechanics issues people were having; though, much is to be said about people doing riskier things with mechanics because of DPS but eh.
And the mechanics usually had enough randomness associated to them that your strategies didn't just have to work on the average pull, but each mechanic strategy also had to have all sorts of failsafes and precautions applied to maximize the chances of surviving, even if you got random ass bullshit RNG edge cases like tethers showing up on the worst possible people at the worst spots.
Tethers, yeah, though it's as simple as tanks work their way around to an immobile target. I think the whole passing error made it more hectic than it really was? Like, if you had to do a long run to get a tether, there was a lot of "WHAT IF IT ACTS UP" rushing from both sides which led to the desync. Maybe if they can ever get to silky smooth tether passing stuff, we can see something like this again since it's at least an interesting take on a tankbuster imo.
Digititis, though, we had down to it didn't really matter who got which. The plan always worked? It's a lot like A12S inception debuff checks of needing to check all of like two total people, yourself and one other priority person and go from there. Wash Away Digititis was always the worst thing to me :|