Anyway, the VDSL/ FTTC connection is much more stable, albeit too slow for my liking.
Yes, if the coax DOCSIS network is oversubscribed usability collapses very fast. I am lucky to be in the Surrey/Hampshire border franchise, on the Guildford head end, and friends of mine (too far for ADSL originally) have been on this network for 15+ years, without issue. I had some local issues with the cabinet last summer, causing disconnects, hopefully now resolved.
I left Plusnet at the end of 2019 as the upload speed collapsed, having been on ADSL then FTTC since 2004 in this location, the download started close to 60, when I left was just managing 40, but the upload started around 8, and dropped to between 2 and 3, which for my home working was problematic.
So I risked VM, and touching wood, the 200/20 service is relatively stable. I have seen a slow upload of 10 a couple of times. My only other option would be 4G; and I have strong EE and Three signal, the Three service here is very slow, the EE is good, but the lockdown/pandemic has showed how varied these can get. One day 200 Mbps, the next 15 Mbps
21 years of broadband connectivity since 1999 trial - Live BQM