UWC is "the" school for long term expats & locals who have another passport and can afford to send their kids there.
It has a long standing reputation for academic excellence but in my opinion there is more magical thinking in that reputation than actual fact when you compare it to other schools like Tanglin or Dulwich for instance.
It's just that it is the longest established IB program, high proportion of high achieving parents with connections to Ivy league colleges in the US, "we are in a class of our own - reproduction of the elites kind of mentality" etc etc.....
I personally loath that kind of mindset but it does produce good results.
I know dozens of people there, don't get me wrong, very very well turned kids but there you go, there is a mindset within the parent community ( many of whom I do count as my friends).
IB is not subject based so schools have a wide latitude on content ( you need to research IB to make up your mind). In broad strokes, a school with a very solid reputation and faculty like UWC will certainly deliver a solid basic literacy and numeracy foundation similar to UK key stages and stream ( and push) kids appropriately if so inclined.
I would hold my breath on a school that was newly transitioning to IB as the primary years program if not properly delivered by experienced teachers can leave you open to gaps at the end of primary.
That said, since Dover has been delivering a standard UK curriculum so far I don't expect it would be too much of a problem. Tanglin did that very well a few years back. As long as existing admin and faculty are are valued in the transition period.
I really don't think you can go wrong with any of the schools you are looking at right now. And you certainly do have time on your hands as you are still a couple of years from Y1 when all those thing really start to matter. You still have time to play the waitlist game. You can move them when you have more clarity on your mid-long term plans and if you feel the bigger through train schools are more appropriate for your situation.
We really tend to overthink things when they are so little. Just secure a place where you feel you belong as a family and take it from there.