I still think stats in general need buffing. It should go something like this:

All tieflings and druids = Level 3 or less

Nettie and Rath = Level 4, so roughly on par with the PC party or slightly weaker than the party by the end of EA

Kagha and Zevlor = Level 6, because Rath wouldn't even challenge Kagha, but kinda sorta debated it, or so it seems. So she should be maybe a level or 2 above him. Zevlor and Kagha seem more like peers in EA, and Zevlor is. Hellrider Exile, so we know he helped defend Elturel in Avernus and became a Hellrider at that time. He should not be easy to kill. Man was fighting devil's and such for who knows how long.

Gut = Level 6. She seems the weakest of the Goblin Bosses, but she's supposed to be a Mighty Booyahg who can put limbs back on - an exaggeration I'm sure, but she should still be tougher.

Olodan, Ragzlin and Minthara should probably be Level 7 or 8.

Halsin should then be Level 10 minimum. This would be assuming Halsin is just a small time First Druid and not really an arch druid. He's just the best and wisest. I could maybe believe that. But still, based on story, Level 10 or 11 would fit much better.

Oh, but wait! How will anyone defeat any of these powerful characters?

The way that makes sense. You don't 1v1 them like in most video games where somehow the weak hero is able to still defeat the insanely powerful enemy in unbelievable 1v1 combat.

You gain allies to help you, like gaining Halsin as an ally against Ragzlin and Minthara and Gut. You do quests like fight the Hag to gain more experience and higher levels so you stand a better chance in the fight. You get Rath and other druids to help you against Kagha and Olodan, or you turn Kagha against Olodan and gain yet another more powerful ally to make the battle less difficult.

You find ways to weaken your super tough enemies, like setting traps. Larian could provide special ways to help damage them more powerfully, such as - wait, they already have some of these kinds of things in the game - drop chandeliers on boss enemy's heads to pin them down for a turn or two while you wail on them.

There are so many things you can do to make fights more even without making it so that these supposed bosses are so weak and easy for a party of 4 to kill. Right now, as it stands, the last several times I reached Ragzlin and Gut, and even Minthara, the fights were so easy I barely broke a sweat. The Githyanki Patrol fight was WAY more hard than these three supposedly tough bosses.

Anyway, it can be done, and I'm REALLY hoping Larian does something to make them more true stat-wise to their characters. Then I hope they sculpt the game around this so that we have to do some thinking to overcome the challenges that they should be.