Am I off the mark but buying gems seems like a really bad investment?

So I'm a new player and I'm happy to buy gems in games to help myself out. I followed a few YouTube guides to get basically a meta deck and as per my last post, I also crafted all the "hand traps" I needed.

I'm nearly in gold rank using an upgraded Blackwing deck but I want to craft the last lot of URs I need to finish off my "meta" deck so figured I'd check out the gem store.

This to me seems like I'm paying £15 for 20 packs of cards. Is this correct? If so, once the welcome packs are gone it just seems to be even worse in terms of what you pay Vs gems back?