Uhtred unreasonably punishing to melee unless I'm missing some kind of mechanic

I just (tried) to fight Uhtred, one of the Expedition bosses, for the 2nd time this league. The first time I was very poorly geared for the level of logbook and so I didn't draw much inference from him wiping the floor with me.

This time, I was much more equipped. I'm a jugg with 7 endurance charges and minimum 10 crab barriers scaling up to 15 for 1.5 seconds out of every 4 (so 20-30% extra phys mitigation on top of endurance charges). I have maxed elemental resists. I have significant hp regen bases, increased by Unbreakable due to boneshatter self-damage even when not taking enemy physical hits. Capped standard resistances, though a lot more tanky against elemental damage than that would imply as I just transitioned to divine flesh this morning with 89% max chaos res, so nearly 30% less elemental damage (and closer to 50% if the hit has some manner of elemental penetration due to how divine flesh works). I had to drop a bit of life due to the divine flesh transition, still had 5965 hp.

His initial mechanics seem extremely punishing to melee but in the vein of some other bosses and definitely doable with my gear, though I still had to manually dodge "futile" balls, the puddles from the stars that spawn right from the boss so trigger instantly, the rotating beam and the wall lasers because they all still hurt. Overall, at this point it was an extremely annoying fight, given the low uptime on the boss, especially since he appears to have Ward, but really this isn't the only boss that fucks with melee like this and I wouldn't be making this post if this was all there was.

The real issue is that in the second phase, he started using a mechanic where he shouts "Insolent whelp!" and spawns a wall of moving ball projectiles. These instantly one shot me. And by instantly, I don't mean I saw them coming and didn't dodge and died. I mean he gave no apparent forewarning to using this skill and spawned them right on himself at the beginning of the voiceline, so I was dead before he even finished the first syllable.

The logbook is blue with two mods that don't increase difficulty for my build at all. I used to think that remnants impacted bosses (and they definitely did for medved), but then there was the patch a week or so back which noted that remnants were incorrectly treating medved as a runic monster. The only logical conclusion I can come to is that remnants that don't specify runic monsters, like penetration mods, might still impact bosses, but I specifically didn't choose any penetration mods on this fight, the only mods looking at the list which would impact boss damage at all even if applied was a 15% generic damage mod and 50% phys as extra chaos (and again, I have 89% max chaos res so that's not nearly as impactful as it sounds unless he has some sort of in-built chaos pen AND the spell used was physical, which I find unlikely given how it one shot me as a full flat physical mitigation jugg).

I'm finding extremely minimal online information on this boss's mechanics at this point, so it's possible I'm missing some sort of not-very-obvious forewarning to this skill. However, it feels like this boss was honestly designed without considering melee even exists if there's an instant oneshot mechanic that spawns from the boss's frame without forewarning. I really like this league in general, but one of the main bosses of the expansion shouldn't gatekeep an entire class of characters.