I’ve found this to be a DPS check. Basically, all of the group should hit the same burrow. No defenders. When it is down, move to the next. With enough DPS and swiftness, there will never be more than 1 burrow up and the gravelings will never reach the collectors since you intercept them as they get out of the burrow.
If a pack of gravelings heads for a collector, hit them once and kite them to the burrow your team is hitting. It’s important to hit the burrow and the gravelings at once, or else pretty soon you will be overwhelmed by the burrows.
I’ve seen people saying that you need to concentrate on breeders before moving to the next burrow, but IMO this is a mistake. Kite the breeders to the next burrow and fight them near or on top of it, such that the whole team is hitting both the breeder and the burrow at once. Otherwise you will have to deal with 2+ burrows at once and this is where teams get overwhelmed.
If near the end of the event, you can’t keep up with the burrows, split into two groups. At this point, you are trying to keep the gravelings off the collectors until the event is complete.
The burrows are easier to hit if you keep moving while attacking (melee). Once their “hitbox” is fixed, these events should be easier, but I think the same tactics will apply.
Edit: What I mean to say is that, with the correct strategy, these events aren’t too hard. I don’t think they need to be made any easier, apart from fixing the bugs when targeting burrows.

(edited 14 days ago by Demosthenes.4635)