It's Lewes and it was never a 'main' route. FWIW with the station building and single platform feel about right for a single-track branch line and the town itself - it's not a grand regency resort, after all. The car park on the far side of the road (i.e. the original station site) has been laid out to accommodate 2x 12-car platforms, should they ever be required.
The Bypass didn't solve the crossing issue - anybody who's sat at the lights without the crossing will tell you the level crossing would be a total disaster. Housing development in Uckfield won't lead to rebuilding the link to Lewes, only housing development in Ringmer, a massive windfall for decarbonisation or a major drop in rail project cost will achieve that.
My personal vote was for Portsmouth Harbour, but if Uckfield counts as a main route then I'd nominate Seaford - having departed either Brighton or London, and skirted the downs for most of the journey, you get a lovely run down the beautiful Ouse Valley. And then you get to Newhaven: incinerator, industrial port and all. The pitiful survival of the original station buildings just add to the feeling. Then the single line, Bishopstone with it's abandoned platform and Seaford with it's only platform numbered 2. Set up as a through station, for a line that never got built and now never will. It just feels forgotten and uncared for.