Is this "boss" soloable?
Or is it quite a hefty boss that take a few people to kill?
You can solo the boss. It is an instanced zone meaning you can go alone or with a group and you don't have to fight over it, that requires about a 5minute run to get to. At worse, you can 2man it if you're not strong enough. You can do this on as many characters as you like, once per day.
They likely did the 40+ version, there's a 22/33 version.
I think it's a bit upsetting that a 45 wep dropped before a 43 wep has ever dropped, from a boss that can be solo'd with no competitive aspect to it. Likely a mistake on their behalf, wondering what's going to happen.
What's more upsetting is 90% of bosses ingame feel worthless to kill in general, people grinding bosses over and over in hopes of a 43 wep (or just more 40 weps/gear/spells) and sadly most of it comes from mobs, then this happens. I can see why people are annoyed.