With FADEC engines, nearly all the differences in accel rates are when coming off idle. There are various control laws that limit the engine accel rate coming off idle - depending on engine health (mainly compressor efficiency) and even subtle differences in idle speed, you can see meaningful differences in accel off idle (we investigated a few 747-8 differential accel RTOs where not all the throttles where on the idle flat when they initiated the throttle push) Once above idle, the FADEC control laws revert to what's called "N1dot" (rate of change of N1) - or EPRdot - which relate directly to thrust - so thrust asymmetry is minimal.