I'd keep two cards. But not these.

The PP is at a reduced rate already due to Lifetime UC, and you get $60 against the MP Explorer as a 1K. However, if you can cancel MP Explorer, and get Chase Sapphire Preferred, the $60 credit should go to PP.

I'd ensure I spend $25K a year on PP and spend on CSP for the great 2x/3x bonuses offered. Once your miles are in UR, you can transfer 1:1 to UA MP, plus a 7% bonus.