I think one of the main things behind all of this is that Arriva are never really ahead of the curve. Sapphire, for example, was always just a poor imitation of Stagecoach's "Gold". WiFi and on-board power only started to appear, iirc, after Go North East had offered it on some of their premium services. 

I think the one thing that strikes me most often is that, every summer, the X18 has the potential to be a immensely popular route. It is popular and very well used, don't get me wrong, however every year they run *very* late, all day, every day. While 7529-33 are very pleasant vehicles, that's one less than the summer PVR, and the summer spares the past two years have been in the form of 4664 and 7416... The route still has no NSAs, and for a potential 4 hour journey, no power is quite surprising. 

The X15 is another example. While I still believe 7511-3 are capable of the route when working, the amount they seem to be VOR now is not acceptable for the route. Their sister vehicles have just been taken off a far less demanding pair of routes, and while those 3 were in a better condition to begin with, 4 years of solid flogging up and down the A1 hasn't done them any good. New vehicles are badly needed, and they don't seem to be forthcoming. On that note, I contacted Arriva last summer complaining about the service, and asked why the service didn't have newer vehicles when reliability was so poor. Their response was that they were moving more powerful vehicles to the service from October... did they break down before they even got there?