... the Intrepid is faster and more maneuverable. It's also newer so it has more advanced technology like the gelpacks
The thing there is, if the gel packs (or any new equipment built into the intrepids) were shown to be of an advantage, the gel packs would be retrofitted into all Starfleet vessels. Not just the galaxys, but also older ships like the excelsiors.
It's not like the various ships would have to be physically torn apart in the process, just find room and install the gel pack system, "hard wire" it into the existing computer system.
Something like the defiant might have trouble finding room, but not a ship like a galaxy.