Well, 'once a year' and 'once a month' are both regular. But the latter is better than the former, no?
A 'good' university's career service will have skills workshops, CV sessions, individual coaching. Access to a diverse set of employers, especially to niche ones which aren't on all the big graduate websites like TargetJobs.
'Regular' means several different career fairs, targeted at different fields/degrees throughout the year. Individual panel events outside of the career fairs, organised by the career society or student bodies.
I went to an 'RG' university and I had a lot of support with personal mock interviews, CV review etc. Also got to speak directly with a lot of employers and attended many insight sessions.
DP went to a not very well regarded university. 2 career fairs. One STEM, One not. One CV skills workshop. 2 career 'advice' sessions. A few big employers at the career fair, but mostly small regional ones. No personalised support, no mock interview, CV coaching., advice on internships etc.
And it shows! He was one of the few to get onto a major graduate scheme, despite a very marketable degree (Computer Science). Most of his friends have no ambition. They live at home and work for small companies.
Now as an employer I do a lot of graduate outreach and recruitment and sadly nothing has changed.
I don't buy into the principle of 'elite' or otherwise. Some not well regarded universities, in 'general' are excellent in their area of strength with placements, close links etc to specialist employers. This doesn't mean it's equally as good for students studying different subjects.
For people like the OP's son it's important to get into a university with good links to a variety of top employers. And as an aside, it's doubly important for people without the connections, like me. I did not know this whole world of graduate jobs existed until I went to uni and benefitted greatly from the atmosphere. If nobody had told me as explicitly as my uni had I wouldn't have achieved my full potential.