Teaching can be very research led which means it's high quality. However non Russell group emphasise teaching more, they employ more staff on teaching only contracts. If your child needs more directed learning then a non Russell group can provide better teaching for them.
It's horses for courses.
A top grade 3 A's student studying sciences or traditional arts subjects is better off in a Russell group they will get stretched more and their peers will be of a higher academic level.
It's like sets at school. Top set needs different teaching at a different pace. They get the teaching they need.
Non Russell group can actually spend more time explaining things in more context and will tackle the subject differently with a more applied focus for example or just with more teaching hours in smaller groups.
The grades needed for the course ls reflect the teaching style. Lower grades achieved mean those students need a more applied and slower delivery. They can then over the three years develop fast and catch up their Russell group peers. Some just prefer more applied to real life and less theory.
It's also very dependent on subject and university.
But generally big Russell group have less smaller group teaching.
Your child will find the right uni for them. The grades they achieve will point them in a direction for the type of teaching they will need to thrive.
We can't teach a class of 3A's in the same way as a class with lots of 3C's.
So Russell group will go faster and be more theoretical in approach and also expect more independent learning.
Non Russell group will spend more time with students going over key concepts.
It's just different approaches to fit the student.
They all cover similar content in the end.
Russell is more academic. For most jobs though that doesn't necessarily matter.