if you choose the lest side you'll have the benefit of fighting enemies one-by-one. cuz there is only 1 voidwoken per wave.
That's what I did (or tried to do) when I first got to this part. I clicked for the party to move up to the rampart to the left, but only my main made it up there, because combat started at the same time she was climbing the wall. Given my experience playing this game on Tactician, I suppose I could have been smarter and had the entire team jump up from afar instead of climbing.
But here's the thing: you would have to separate all your party members first, then have them jump up one by one, while the Voidwoken murder the magisters. I guess it's my fault that I try to role-play a bit and rush to their rescue. I simply didn't expect that approaching this encounter casually on ground level could lead to such a huge disadvantage for the party. Disadvantage is one thing, but it's just that it feels unsatisfying, the way it happens.
AFAIK, it's possible for two suicide bomb Voidwokens to show up at the same time, one after the other. Probably it happens if you kill two or more Voidwokens in a turn. It happened to me a couple times. Once two of them went for Beast and did something like 4000 damage, almost killing him.
As for the "waiting for all magisters are dead" strat, I suppose it's just another fault of mine. I'm one of those players who care about such things. The point of the encounter is to save them. So I don't want any of them to die. I know my personal ways of doing things make things harder than necessary at times. My whole point is that, this encounter could've been implemented in a way that induces less frustration, while still keeping it challenging. Also the fact that, if you don't take full advantage of metaknowledge, the whole thing can be a rather bad experience.