Somehow didn't see this thread before, so here are some comments as a user of the Hertford Loop.
As mentioned, this removes most of the immediate justification for a TfL takeover. They did a terrible job with the Lea Valley lines (it's always the NLL & ELL which are the success stories), and the only thing they could do better here immediately is to have a dedicated driver pool. Last year I would've seen that as a big win but reliability has improved remarkably on the Inners and I can't really say driver availability is a problem anymore.
The peak frequency as far as Gordon Hill is not going back to 8tph. Previously ETUG quoted a GTR representative who said this was not possible for reasons unknown. With the current 6tph peak service now being quite reliable I think it is a missed opportunity given that even without cancellations Hertford trains get crowded. However a bigger oddity is that, like now, there will only be 6tph as far as Gordon Hill in the evening peak but all the way to Hertford in the morning.
All trains down the Hertford Loop will stop at all stations unlike 2019 (the timetable already published on Rail Record confirms this). I have a neutral opinion on this - it does make the service easier to manage in disruption and also ensures a clockface timetable everywhere but I think it would've been worthwhile to introduce a semi-fast service to Hertford, calling at all stations from Moorgate to Finsbury Park, then Palmers Green, Winchmore Hill, Enfield Chase, Gordon Hill and Hertford North. This links into the problems with the Finsbury Park to Ally Pally section which I describe below. Ideally loops should be constructed at Gordon Hill to allow a true fast Hertford service but this is too off-topic.
I see the popularity of the Sevenoaks service has been mentioned. This is not mainly because it goes through the TL core. Rather the biggest factor is the it starts at Welwyn and provide 16 empty carriages an hour in the morning peak, in addition to the long-existing 24. I'd go as far as to say the Welwyn terminators are more popular than the semifasts at peak which often have no more seats free by Welwyn GC. While not running these services all-day
or running 4tph to Moorgate all-day is a loss, I think stops could have been added at Brookmans Park & Welham Green at least. Nothing in the timetable requires these to be skipped for pathing (with the semi-fasts) reasons. Similarly they need to stop at Ally Pally and stops from Finsbury to Ally Pally need to be rationalised overall as I explain below.
Finsbury Park to Alexandra Palace is still a mess because Harringay & Hornsey do not have platforms on the Up & Down Slow 2. This results in a weird mix of stopping and non-stopping trains. Many Moorgate-Welwyn trains do not stop at peak which results in this awkward arrangement in the evening peak of (from Finsbury) Platform 8 -> DS2 -> DS1. The ex-Sevenoaks trains do the same thing. Instead this section should get a simple mostly clockface service, with 4tph Moorgate-Welwyn, 4tph Moorgate-Stevenage/Hertford, for a total of 8tph, and the additional 2tph Sevenoaks-Welwyn for Ally Pally. This would allow much better use of the US2 & DS2 as Hertford trains would be the main users of them instead, which is physically much more sensical.
I'd be looking for 2tph Welwyn-Sevenoaks and 2tph Crews Hill-Orpington with 4tph Alexandra Palace-Bromley South.
I agree that these pairings are very logical but it is important to keep in mind the fact that Moorgate is uniquely a dedicated terminus for the Inners. The aspiration with the 717 order was to run a 10tph service from Moorgate to Gordon Hill and there is zero reason to introduce a Thameslink service until this is met; it would be a waste of a dedicated fleet and a dedicated terminus. New Town users of Crews Hill will not plan around such a 2tph service, they will just change at Finsbury for the core if needed (especially if Sevenoaks eventually becomes all-day as you seem to suggest), so this needs to be seen as a way to bypass the capacity limitations of Moorgate which have not yet been met, not as a way to improve connectivity. A 10tph service will not be enough in the long run but only then is a Thameslink service (as well as platform lengthening) worthwhile looking at.