I guess you'd have to imagine the PTBNL would be better than Lacy. Hard to think Lacy would be the lead prospect in a deal like this, even with Hamels not pitching well and with us covering some salary.
PTBNL in trades like this often are determined in part based on how well the named player or players do. Hamels does well, and TX picks from list A made up of a few decent prospects. Hamels stinks and they pick from list B which is made up of guys the Theocracy might be considering giving their releases to right now.
Appears to be little more than a salary dump, with Hamels not likely to produce anything more than league average pitching.... but even league average would be better than what they have been getting from the 5th spot and should help win a couple more games with the Cubs' lineup. Hamels is not really likely to play a role in the post season rotation, but he is insurance in case another starter is lost, and if he is just good enough as a starter to reduce wear on the bullpen, then could be of serious value during the playoffs.
Looks like a good move for both teams.