Having worked in the middle east and far east also as quality assurance I can assure you the reasoning is quality.
These bases have been able to and have accepted any licence in the past. There have of course at times been language issues but the main problem was not even their skills, it was their safety culture or rather lack of it in comparison to your average Brit or Aussie.
So yes you are right, I can give any European a screwdriver and ratchet set and they will do the same job. But ask about safety and consequence of action or lack of action and most Europeans are left looking at the ceiling.
Ask about reporting systems or competent NAA's that provide buckets of useful information and you soon realize that the stipulation about UK licence is from a quality perspective the right one. Whether it will withstand a discrimination challenge, I don't know.
The point is, being liberal is great on the one hand but very dangerous on the other. In utopia we would assist our European colleagues with their safety culture and not knock them. But now with quality of training also going down the toilet I am glad that I have almost reached retirement.
The UK will do what it always does best, nothing until its too late. Thats why the second world war took 6 years instead of months. The warning signs were there for years, Churchill bleated on about it all the time during the early 30's but was just abused and scoffed at.
The UK car industry well there's a story. Anybody see Top Gear the other day. In 1946 the UK exported 98,000 cars to the rest of the world and imported 63. Yes 63 not 63,000. The warnings signs were there in the late 50's early 60's that the world beating UK car industry needs to pay attention. It didn't and disappeared.
The UK licensing situation is no different. You can play the liberal if you wish and play up second rate engineers as being equal, but you do so at your own cost.