My DS went through all this recently as he has just completed the first year of his Maths degree
Everyone in his FM A level class took 4 A Levels as did everyone he knows on his maths degree.
So I can only advise from first recent hand experience.
I wish your DS all the best @Cratos
If he wants to drop Economics then he should
Yes it’s great to get into Oxbridge but even if he takes 4 A Levels and gets 4 A stars there’s still no guarantee
The top Maths degrees at COWI are very desirable and many apply. But in turn they are more difficult and have a lot of content. The next level down uni wise are slightly easier. DS has friends at various unis so they compare.
Choose the uni and modules in the degree that will suit.
My DS has found his first year at a COWI uni fairly easy to navigate whereas many students have found some modules horrendously difficult.
call admissions, read PP posts, read the links 🔗 and other threads for advice.
Maths degrees are competitive so do the best you can to get into the top unis for Maths but you do need to like the feel of the uni because that’s equally important.
We have loads of great universities in the UK and not everyone chooses to take up their Oxbridge places because they change their minds on the course content or decide to do another subject entirely.
DC have to be true to themselves and the rest will fall into place.