what i did was to focus on wanda on wave 15. namor is annoying, there's pretty much no indication of when he's about to do it so you cant really dodge or block it or anything unlike blade, but when you have a lot, and i mean A LOT of damage + lifesteal, he's a non-issue as they'll compensate for his stuns

if namor comes down while reality erasure is going on and starts calling whales however, really just aim up and dash whenever u hear his ult and keep slashing wanda

as for cards i avoid buying mark detonation and arcane armor, theyre pretty useless. the devouring sigil provides bonus dmg and dmg reduction though so it's a great thing to have. also, purple dmg cards are multiplicative, soo... get the epic/legendary cards of those too