I've spent a long time with folding bikes over the years. My advice: bite the bullet and buy a Brompton[1]. Yes, Bromptons are expensive. But they ride like a bicycle, have gears, a stiff enough frame, luggage racks etc. There's very little compromise. The fastest I've done on mine is 45 kph and I've ridden 70km in a day. I carry it on and off buses and trains multiple times a day without issue. In the past I had an…
I'm very happy with mine, and it has most of the advantages you list - luggage rack, real bike feel (my longest day is apparently 64km and top speed 64kph). The sensitive steering takes a bit of getting used to the first time but you adapt quite quickly. For me the simple fold (and, sure, lower price) feels like a big advantage compared to the Brompton, which is what several of my friends have.