Could quibble about sub-speciation of trains and boats but this marvellous. A great day out. Shame we can't all get stuck on a Boris zipline to round out the day.
My main quibble would be that Thameslink is definitely National Rail. (I think that the Elizabeth Line is too, technically, but the transverse seating and the platform screen doors, and the fact that it's operated by TfL mean that it's different enough that I'll allow it.) I'm not sure how I feel about the Overground.
Been a long time since I was trainspotting (yes, I had the anorak and the Ian Allan book of rego numbers. London had the western region hydromatic diesel warship class locos. amazing) but IIRC the London overground rolling stock has to be quite different as the tunnel sizes even above ground don't meet normal BR rolling stock radius for turns. If Thameslink runs on special sized rolling stock I'd admit it, but if's general size, any train, I think I agree. Its just another national rail line.
Unless it's a weekend when, if you don't live centrally you'll find out it is "closed for engineering works, as it was in 2024 and it will be for 2025 and so on". Never any transparency. Seek alternative routes.
We only care about providing transport when the lemmings go to work.
While the trip itself is amazing, it could easily be fleshed out with attractions along the way - favourite eateries, boozers, playhouses, gardens etc.
Well done!