@Stefan Mikes I must just have very limited hip flexibility. Like others here, I have always mounted and dismounted a bike by standing on one pedal and swinging my leg around while moving slowly. I've been doing this all my life and have never fallen while doing it, but recently some doubt was put into my mind about whether that was safe "at my age" (74) even though I ride with guys in their 80s that do the leg swing.
Anyway, I tried your method yesterday on my Vado 4 and can get my foot over if I really
kick my leg (not simply lift it), but I can see that I could lose my balance that way if anything catches. In fact, my Crosstrail is similar in geometry to the SL and this morning when my group of guys were going on a ride, I went to get on using that method, lost my balance a bit, and looked like an idiot as I tried not to fall or drop the bike. I didn't do either, but this is not something to practice in front of a group of your friends who start asking what you are trying to do!
The other thing is that on yesterday's ride I went out to the dealer to talk about getting an SL (5.0 ST), which they don't have and probably won't get for a couple of months. While there, I saw that they had a regular Vado ST so I went to it to see how easy a step-thru might be. To my surprise, it was not much easier than doing it on my non-ST bike! The top tube slants up from the seat tube at a steep angle, so most of it is not nearly as low as it looks from the side. When I got home, I even tried mounting my wife's Trek Verve+ step-thru and that too was not as easy as I expected. The next time we ride together, I'm going to ask her to show me how she gets on and off, but I think it's much easier for her since women are generally more flexible and she also does more stretching exercises than I do (and is 10 years younger).
Anyway, I'm now rethinking the whole SL-ST thing again and might just change my order to the regular SL frame version. That way I can also order the non-EQ instead of having to pay extra for an EQ and then removing parts. I'm going to post a new thread in the forum to get some comments by ST owners, but it sure seems like if a non-ST bike has always worked for me, why try to "fix something that's not broken"?