Derailleur/chain not tight enough in highest gear

I just finished upgrading my drivetrain and found that the chain isn’t fully tight in the highest gear. I’m thinking: b-screw, too long chain, or something inside the derailleur. When setting the chain length, I erred on the side of longer (+2 links method…). Another change was the cage length: I went from long to medium. I don’t want to mess with the b-screw since shifting is dialed in, but could.

Any tips? Would it hurt to shorten the chain by 2 links, if that would leave me about 1/2 link on the shorter side?