The key word is ‘numerical’.
Maybe you’ve yet to see or do numerical analysis of both general relativity and quantum field theory but they are in fact both linear algebra.
Which as you point out is “fundamentally more accessible”.
Source: I'm a Physics PhD
Now, GR or at least the core of it is a lot easier as long as you’re mathematically prepared for differential geometry.
Btw, I took particle physics from the Peskin in Peskin & Schroeder when I was an undergrad. Everyone in the class (like four of us by the third week?) was super duper lost by midterm.
The same is true for quantum field theory. I'm curious why you're so confident that they are "in fact both linear algebra"
When talking to a musical educator complaining about struggling students just starting out I’ll say “I found it extremely helpful to paint the C major scale on my guitar when learning music theory.”
And they respond “Well what about chromatic 12 pitch atonal music?! What would Anton Webern say?!”
Some subjects are just plain hard and only accessible to smart persistent people.
GR and QFT definitely qualify - but they seem to be warm up exercises compared to whatever Quantum Gravity will eventually become.
I call you out. Don’t think you’ve done either one after reading your comments.