Slow buffering doesn't seem to happen for me using chrome with AdBlock and AdBlock for YouTube enabled (at least for this video). However, chrome has been telling me to update its version for a few weeks. So maybe Google decided to do this with the latest version of chrome.
You wouldn't download a car, so why would anyone block an ad? Surviving by obscurity, I use Opera, I can watch all those YT movies (free with ads) and I don't see any ads.
The amount of ads on YouTube is ridiculous. Worst, the ads I don't like to see (eg trading/investing nonsense) are shown frequently, and the ads I like to see (eg sexy babes) are rarely shown. Somehow, Google knows I am logging on to my Charting software and my trading platforms. If I want to watch YouTube, I use BRAVE without logging in to my GOOGLE account. So it is ad-free.