Hartland is still a building sight so it is impossible to comment. Wellington Academy...there are actually more than one, El Khail, Silicon Oasis (and possibly more) so you may get more information if you specify which
Both of those that I have listed are fairly new and very big schools. I think First Point opened last September.
As most established schools have long waiting lists for most year groups it is unsurprising that you are more likely to be successful in these newer/brand new schools.
Hartland will be organised in ks2 more like a UK prep school where subjects are taught by subject specialists (like a high school).
The GEMs schools are all international schools that follow the British curriculum, possibly with the IB in secondary.
I apologise that I haven't actually been able to give you any specific recommendations but hopefully given some details that may help. Good luck with the search.