I remember the polyps used to have a long time between respawns (the wiki says at every stage of the boss fight) and it was possible to just kill the polyps and minis and then damage the royal jelly without needing poison at all. But now I noticed that the polyps basically respawn within 2 seconds of you having killed them, making it impossible to cut off the royal jelly's supply of minis. While this isn't a problem on the first stage, as you can use poison to stop him?/it? from healing, during the second stage (when he turns into a gelatinous katamari of doom) it becomes basically impossible to keep him constantly poisoned, and he'll end up healing more than enough just by picking up the minis he rolls over. As a result, the only option left is to out-dps his healing, which is also near-impossible even with a Nightblade (not sure about the 3* Dark Retribution though). Are new players just going to have to let higher leveled players carry them through this boss?
Addendum: I found this which might be relevant.
I remember out damaging the Royal Jelly with a 3* Nightblade in Dusker armor. I'll test it again tomorrow. Thinking back at when I was a 3* knight, I think I only did the starvation method once, and my allies could have probably handled it without starving him. Even before the Brandish charge rework I remember taking down the Royal Jelly with my 2* and 3* friends.
It's worth noting that the Royal Jelly actually has 3 phases. There is an audible crack and you'll see a crack on the Royal Jelly's crown to signify the second phase. The polyps respawn at the start of this second phase. I'm skeptical that the polyps respawn as fast as you seem to think (however, I will double check myself).
EDIT** Forgot bout this post! Anyways, I'm back from testing the Royal Jelly. What I found was this.
In short, yes you can still starve the Royal Jelly. However, upon triggering the second phase, the polyps respawn. They also will slowly respawn on their own, but this only seemed to happen in phase 2. I didn't try starving the final phase tho. In retrospect I probably should have.