As far as the medical unit goes at DVLA I only had the one dealings with them when I first became disable in 08 and had a compulsory notifiable event to contact them but back then it took just a couple of weeks to sort through the postal services we had then but unlike the one we have today.
What I want to say about using the DVLA online services with regards to renewing your licence every 3 years once you’ve got 70 years on your clock is using the service in late 2021 I filled the online form in on a Thursday and believe it or not had the new licence on my door mat the following Tuesday. Like I’ve said I don’t have the medical notification bit with them so that helps I’m sure but if its just renewing because your getting long in the tooth then online works well. Just to note though you can only apply for the new license 90 days before your 70th birthday as I was eager and started the process at 92 days and after gathering all the info they need got the knock back because I was too early. ?