Magic: The Gathering Arena - Another MtG video game

What’s the best strategy for building decent decks without putting a ton of money into the game? I built mono blue a month ago but I guess the meta adjusted because I’m finding it hard to win with over the last couple of weeks. I also made improvements to the prebuilt white deck so that it can compete, but it’s still kind of bad against more refined decks. I spent many of my uncommon/common wildcards to build the mono blue, but I still have a bunch of rare and mythic wildcards that I have been afraid to spend. Should I just wait for the old sets to rotate out at this point? I have a decent collection of the two Ravnica sets at this point since I play as much draft as I can as well as getting those packs as rewards. But I’m getting bored of my two decks losing frequently.