It's a little more setup initially, but it avoids having to change your physical pedal arrangement and should give the A320 the single-axis input it expects.
If the aircraft is effectively at its aerodynamic or certified limit, there’s probably a good reason it refuses to accelerate further. It would be interesting to compare the indicated thrust, drag, temperature, weight, and any Mach/overspeed protection or FMC speed constraints to see exactly what is limiting it.