Isn't that the same kind of limitation that UMC and SMIC have to deal?
Nope, both have retained fully-independent internal R&D teams for node development, same as what Samsung did.
Very few companies joined the IBM fab alliance in a 100% committed and dependent fashion.
Many chose to join the fab club as a way of keeping tabs on what others were doing, no different than joining other industry consortium's such as Sematech, CEA-Leti, Imec, etc.
To my knowledge, GloFo is the only foundry in the world that is dependent on external R&D development for process node. Of course they have a skeleton crew of R&D folks positioned at Fish Kill but that is a very different situation than what we are talking about when discussing why Samsung has options which GloFo does not have.