I find I instinctively prefer the online model. I was a bit of a shrinking violet at my Oxford interview 30 years ago and found the strangeness of the surroundings and the confidence of fellow applicants truly alienating. It time travel was a thing and I could have done it online I suspect my interview performance would have been better. Of course in one sense that just meant it wasn't the right place for me, which as Oxford was at the time it definitely wasn't. But if widening participation is the goal, then something that allows applicants to interview in familiar surroundings might be helpful. You can still weed out those who are intimidated by robust intellectual challenge with careful interviewing, and the online interviews are still stressful and high stakes. And successful applicants will at least know they had been 'chosen' when they finally turn up IRL and have to come to grips with the place.
I was going to say that maybe applicants should be allowed to say which they would prefer, but if standardisation of interviews is the goal that wouldn't work. I think Oxford and Cambridge are genuinely doing their best to make the process as fair and equitable as they can, which means thinking carefully about what might suit an absolutely average Jo or Mariam from Northampton whose parents didn't go to uni. Nothing is ever perfect of course.