This is going to be unpopular view but as a neutral who just poked around capfriendly for a bit...
Before the trade, the Kings really had no long term option in net. That was supposed to be Cal but Cal has been terrible and he's in the minors. And Kings also have no cap space next year. Quick was coming off the books either way, but Mikey Anderson and Trevor Moore are getting raises, that basically takes care of the money that Quick was making.
So -- no goalie, no cap space. A legitimate top tier ELC goalie would work but good luck getting Dostal or Levi or any of those guys. And even if you got someone like that, maybe they wouldn't be ready for full time NHL starter duty anyway (see Spencer Knight).
Joonas isn't the worst idea. Kings are good defensively, you just need someone to be average, that should be good enough. Seems like Copley was good enough when at first, he's slowly been getting worse though so maybe not the answer just yet.
Joonas is 28, that's not too old. He's only making 1.3mil this year, that's all. If he ends up playing ok for you, you can probably give him a 2 or 3 year deal at a 3m cap hit or something idk. And, in terms of goalie quality he's probably the best available right now, good thing Kings got him otherwise maybe he goes to Buffalo and Kings have to go into the summer / immediate future with Copley as your default #1.
But yeah, Kings are good enough defensively imo you only need an average goalie -- Korpi is that, and he's relatively cheap. And all you spent to get him and Gavrikov was a first rounder. And if you didn't make this deal I'd think Korpi gets dealt to Buffalo later this week.
So to me, sentiment aside, seems like a good trade for the Kings. Kings need a goalie for the next few years, maybe it's Korpi and maybe it isn't but at least this way you can audition him and see for yourself. Either way, not sure there are many better goalies who are available now or will be in the summer, esp not at the low cap hit the Kings need