In all honesty, memes aside, I don't see how is this impossible, if anything, it's far from impossible and a 921479821421x improvement compared to the original raid where it's a logistical nightmare to handle.
First of all, this is a raid meant for everyone, even newbies can participate, how good is that? We have members that are legit new players and can't do jack shit to the boss nor meet the level 50 requirement, I'm grateful for the developers in including even the newbies for the anniversary special raid.
Secondly, the milestone rewards are equivalent to the killing rewards because I assume the milestone rewards were meant to be the actual reward and that means EVERYONE is guaranteed a 250, but those who actually managed to hit it gets the bonus 250? Since it's pretty much an easy boss that only requires a minimum of merely 1,500 hits collectively from THIRTY FIVE members, obviously the difficulty lies in the coordination of the guild, and the bonus 250 is the reward for it.
How is this far from impossible? Quick math, 1500-240 = 1260/30 = 42, which means every member just need to hit around ~42 damage to the head and the remaining two guildies can swoop in and clear up 120 HP each, is it easy to plan and talk about it? Yes. Is it easy to execute the plan? Yes.
Finally, like Kitsuneblue said, there is no reason to assume that the devs are intentionally trying to screw players over by making these type of raid a logistical nightmare (which is a false assumption in the first place) , they have better things to do and are most likely busy enough working on future content as well.
P.S. They did screw us over with the inconsistency of the dead left arm that may or may not provide shields for the first day of the raid, but as far as I'm concerned, the whole left arm not giving shield is intended. But after that, with the new information, it was very easy to think of a fail-safe measure to deal with the boss.
P.P.S. I struggle to fathom what will the complaints be if a real challenge were to come, seeing that this trivial issue is already dubbed as a logistical nightmare.