I just noticed this thread, and thought I would weigh in. When I researched and went looking for an e-bike (at age 65 and having been inactive biking for a number of years), a step-through frame was at the top of my list of must-haves. I have a 28” inseam, coincidentally less than the height of a 29” or 700mm tire, so throwing a leg over the top (including the trunk bag I always have installed) would require some high-jumping practice. It makes sense to me with full-size bikes trending more towards taller wheels, that there would be a correlating interest in ST.
I ride my Trek Verve + 3 at least as much off-road as I do on, so I have made changes to it accordingly:
• Redshift Seat post and stem (the sprung seat post that came with the bike was minimally effective and front suspension is not offered).
• Wider ratio cassette, to 11-46 (from 11-36) for better off-road hill climbing, and removed chain guard for quicker access.
• Change from Bontrager commuter tires (soon) to Schwalbe Marathon GT 365 for better all-season/off-road traction.
• More open, knobby pedals.
I regularly ride the bike at 30 km speed, and off-road in the 20’s and have not noticed frame flex to be an issue at all. The battery is in the down-tube at the front. Trek has made provision to add a second battery on top of that tube, but I wouldn’t mount one there. I have removed first a water bottle cage and then a folding lock from that location, as they were just something to hit my knee on when mounting/dismounting. I like the step-through to be as low and open as possible; one of the reasons I didn’t consider a frame like the Allant Stagger or even the Allant step-through.
If I lived in a hilly area, I would have looked for a model with more power (optional?), but it is pretty flat where I live. And I enjoy the added range and a good workout.