> mention that this paper was submitted to CVPR in the comments

I think that publicly mentioning the arXiv preprint was submitted to CVPR is explicitly against CVPR policy. So I wouldn't do this second part of your advice.

I wouldn't make a big deal of when it was submitted (especially since you didn't upload it to arXiv like you should have). You can mention in passing that your paper is under review at CVPR. The important thing to note is that you spotted their work because it is similar to what you were working on and would be eager to cite each other as concurrent and talk to them about the work and future directions.

I think that your supervisor is using arxiv wrong, and giving you bad advice on how to use arxiv.

If theirs came out on arXiv just 2 days ago then isn't your preprint still first? If so, you can email to ask the well known research group to cite your preprint in the intro of their work when it comes out (even if their reviewed version comes out before your reviewed version). Nice way to make a connection, too: 'great minds think alike' and all.

I feel you.

> I see people are more motivated to pursue topics they feel they will be "scooped" on if they delay even one conference cycle...

I also see this often and so I use the inverse of this as the guiding principle in much of my work. If I feel like this is a topic I'd get 'scooped' on if I didn't publish quickly enough then I look for another topic to work on. It usually feels nicer to do 'slow' research. However, it can be a bit isolating.

He doesn't seem to have a faculty job -- but a fancy postdoc at an average school: "Forskare (Research Fellow) in Responsible Artificial Intelligence, Umeå University"

I'd definitely want to see some specific evidence (instead of 'google this') before trashing the reputation of some random postdoc.