Jansen being out isnt the problem. Collins being in over Biggio, when we've just seen Tapia start twice in the OF... is. That's far from optimal. It's doubly dumb now that we know Jansen has mild soreness. Now, you're left with a lower floor lineup and your backup catcher at DH. If Kirk get's beaned, youre left with losing the DH spot, or putting in a guy you didn't want to be in there due to soreness.
THe obvious counter there is, maybe it's not a big deal and jansen would be fine to come in if Kirk get's hurt. Well, maybe, but as your catcher, if you're hurt enough they dont want you starting, they obviously wouldnt want you coming in in case of injury to the other catcher either. This is exactly the scenario whereyour 3rd catcher should be sitting out as a backup and not starting at DH.