At the same time at Portaventura you'll have MUCH more fastrack and those who dont wish to pay for fastrack simply push past everyone.
Swings and roundabouts really, I dont think the disabled system at Merlin parks is to unfair, back in 2003/4 disabled guests could simply show their wristband and skip all the queues, now on the major rides they can not ride another ride for the length of the queue (so for example if a disabled guest rides Colossus and it has a 1 hour queue they will not be able to use their band for that hour) Though this only covers the major rides I dont think its a big advantage as it once was.