Exactly my thoughts. First off this is all a pointless discussion if we don't sign Gallen, the Cubs won't have a decision to make for the rotation until Steele returns and even when he does you never know if someone in the rotation will already be hurt or maybe they go with a 6 man rotation finally to keep everyone fresh during the 2nd half of the season.Boyd is much more likely to turn into a pumpkin.
If they do sign Gallen then the rotation does become crowded but they don't necessarily have to make a move either until Steele returns. There is no denying Boyd had a great bounce back year and stayed healthy, but the previous 5 seasons he couldn't stay healthy and if you look over the bulk of his career he's still a career 4.57 ERA pitcher with 199 starts. Taillon has a career ERA of 3.87 and 223 starts and just 1 season where he hasn't logged over 104+ IP. Much more proven track record and consistency over his career and 1 year younger than Boyd too so I have much more confidence he can stay healthy and consistently productive over a course of a full season than Boyd can.
I doubt you really get much back in a trade for either with expiring contracts at their age other than maybe some kind of salary relief and a low level prospect or 2 that may or may not pan out several years down the road. And for that kind of return would rather just let things play out and decide if someone in the rotation can slide into the bullpen when Steele returns. Beats having to go out and possibly trade for bullpen help if there is a need. Sometimes a guy that moves from the rotation to the bullpen can be very effective when they only have to navigate through 1-2 innings vs trying to go 5+ so they can just let their stuff rip knowing they will not face the lineup more than 1 time through.