I've written for at least a thousand international clients, hundreds in the UK, and this doesn't seem to be a US thing based on the resumes/CVs I see.

I'm not saying people are filtering on seeing "I", but they would be surprised in the same way they would be by seeing third person "Thom is a CTO with..." on a CV.

I have no agenda here. I'm just telling you the facts from someone who has probably read far more resumes than most others. You don't need to accept my expertise. Again, run a google image search on resumes, tell me how many you see with the word 'I'.

You clearly don't value my experience. That's OK. I'm not some advocate for first person pronouns - it doesn't help me in any way that resumes are written in this manner. I'm just explaining to you that it's a fact.