I haven't finished yet. But what about the encounter rate frustrates you? What difficulty did you play on? Outside of having to worry about the boost SP/HP that the Personas give, I haven't really ran into issues of blowing through them in a matter of 1-2 minutes with the boost system.
The first half of the game? Nothing really. The puzzles are small enough that the encounter rate isn't frustrating and there's so many ways to completely break the random encounters (Mudo / Hama spam) that they don't become that frustrating, if not more than a little boring to deal with.
By the last dungeon, Mudo / Hama don't work that well anymore as most of the random packs are comprised of 1-2 shadows that block one or the other and the rest just seem to have much higher dodge capacity. Granted, I didn't fuse Samsara / Die For Me until the last floor, but by then I was just using the "no encounters for X steps" items so I could focus on finishing the god damn game. If I hadn't the final two floors would have easily taken 6-8 hours to 100%.
Plain and simple: The fun in Persona Q is few and far between. Any concepts with potential wear out their welcome with the 10th iteration and 10th hour of dealing with them.