My DD is in her second year of doing a BTEC at college. She would not have been academically up to A levels, and in fact even her BTEC has been a bit of a stretch.
BTECs are worked and assessed very differently from A levels. You may like to skim the BTEC Support Thread to get a feel.
What is his predicted GCSE results profile? What A levels would he be considering?
A levels require a large degree of independent work / self motivation. An unmotivated student can easily crash and burn. BTECs are more steady pace, with more focussed assignments.
You can go to university with high grade BTEC results. imo Good BTEC results may be of more use than poor grade A levels. (Good grade A levels might be of best use generically for someone who doesn't know what he wants to do yet, but that may not be an option for your DC from what you have written).
There are more generic computing courses than Games Design. Something more generic may be of more use. Has he shown much interest in proper programming up to now?
Similarly, what interest / aptitude has he shown for Art/Design.
The trouble with a BTEC is it does send you down a career path, which is fine if you know what you want, but less good for someone as yet undecided.
We have found the pastoral care at college to be way less good than at school. This has been a real problem for us. Also the college had no prior 'knowledge' of DD so I think have been less supportive when we have had issues (as they hadn't seen how hard she worked for the previous 5 years)
Could he do A levels at a larger school / college?
Staying somewhere you are not suited to for friends reasons would be a mistake imo.
Sorry this is a bit disjointed. Hope it helps a bit.