Elevenplussoon
I think you need to consider what you mean by academic, and what this looks like for your son. Numbers applying and where the cut off is will vary by year. City in particular is in a strange position as it is frequently a back up option for Westminster and St Pauls as well as a good option for boys who are less sporty than average for Dulwich College say. They have to make a lot of offers to fill their places. There would be relatively few boys travelling past Whitgift and Dulwich to get to City. Academic boys who want to do less sport have Trinity and Alleyns as good options too.
Whitgift has a very large yeargroup - by 13+ usually over 200 v City at 145. The brightest are very bright. The top sets for each MFL are streamed and have their humanity lessons in those languages - something I haven't seen anywhere else locally. IB as well as A levels are well established and successful. There are a lot of extension opportunities in each department. The school produces dozens of Arkwright engineering scholars, the top sets can do 3 or 4 languages at GCSE, as well as extra maths. I could go on. Academic boys can do very well there. Whitgift have just had 22 Oxbridge offers, City 25.
The lower range of ability will do fewer GCSEs, with the emphasis on getting the best possible results from those, so some boys will only do 8 GCSEs.
Looking at how easy or difficult it is to get into the school doesn't really give you a true picture of how academic it is IME. With most senior schools, you want to get an idea of where your boys might fit within his cohort. It can be demoralising to feel as if you are struggling in a very bright mix.
What I'm trying to say, is that on the whole, especially when looking at the day schools, each of these schools will cater for academic boys. The extent to which they differ in terms of say league tables is not across the top sets, and if you limited Whitgifts results to its top 145 boys, then they would of course be even higher.
So if you are comparing schools I would think about the ethos of each school, and what type of boy thrives there. The difference in terms of sport, and some of the competition that it brings can be a significant one, and whilst both schools are big enough for a wide range of personalities to find their niche and excel, you may view one environment or the other as being more suitable.