Name one in the same position not playing for a club qualified for the CL (because they won't come) that would be a better cheaper option? It's easy in theory, in truth players of Sigurdssons quality are harder to find that is realised. Punting on young or foreign players who might make the step up/transition to the Premiership is a huge gamble, we should make these gambles but as well as proven players not instead of.
Plenty of non top-tier CL players would come to prem for wages/step-up in league quality (see: Klaassen to us, loads more examples over the years).
The other day I namechecked Bellarabi, Berardi, Keita Balde, Filipe Anderson, Ziyech, Lanzini. For £50m the market opens up even more - Oliver Torres, you can even make enquiries on players like Angel Correa at Atletico and see if heads are turned by more playtime/money.
I also totally don't buy the whole 'premier league proven' thing, just about every best player in the league came from abroad, you just have to be clever with it. I don't think we're being clever with our money, that's all.