I think that the problem is very hardware dependent, especially for people using older computers and tablets. Non-static ads often increase main and graphics processor (especially) and memory usage, but the effects can be almost as bad even if you use the most up-to-date software.

My former workplace 'upgraded' their computers from Win7 to Win10, and they were slower and less reliable as a result; my 3-4yo tablet won't run this and many other websites (including and especially the Telegraph) using ANY browser now without having Ghostery, uBlock Origin and AdGuard Adblocker installed - it would grind to a halt if they were weren't, and even when they are, it's still very slow. The ad-free BBC website runs fine, as do many ad-light websites.

My far more powerful (yet 7yo) PC works fine, except for some occasional operational issues with, again, the Telegraph, with or without the ads being blocked, but I use the blockers generally because other website are far worse (including those that stupidly post dodgy ads for fake goods, despite the main website being legit) and I rarely take notice of ads anyway.

The most major issue (especially when I previously had a usage limit on my ISP) almost used to be 'flash' or video based ads that a) used significant processor power/memory and b) contributed a significant amount to my datae usage allowance.

I have not turned off the ad blockers, so I don't know what HJ's site is now like, but I've said it before when it got a real problem a few years ago that the non-static ads should be dialled back, as they really impact on operability of older computers, particularly tablets. Whilst I don't expect the site to be ad-free or to pander to people with REALLY OLD computers, I think that a balance needs to be struck.