There's not much they can do about the grouping that wouldn't cause increased queue times. They intentionally dropped the party makeup requirements for FLs queues to improve the matching speed since you can actively swap jobs within the instance. They would have to go back to more or less filling the parties before starting the instance instead of being able to immediately enter even with less than full teams. In fact they were so adamant about making the changes they hotfixed it in between patches rather than wait for 2.35. I doubt they're going to roll that back. If one of the three parties in your alliance lacks heals, strategize. Use that team to DPS overload the center or have people drop their soul crystals to crossclass Cure etc.