Either way horses who don't know how to deal with a ramp will likely get hurt on it just as horses who don't know how to deal with the step up/step down situations will likely get hurt on that too. Whatever works for the person and the horses safety, there is no better one than that one IMHO.
Neither of my Curlies care weather it is a step up or ramp. The ramp they are more catious stepping up but that's about all. I have found that some other horses are nervous about stepping on the ramp because they are not sure what it is.
I have also read articles that the ramps are dangerous because you lean down to put it up and then a horse could possibly kick you if they wanted. The step ups have been known to trash horses ankles when they try to back out too fast. But, for me, it doesnt really matter. As long as my horses are comfortable in both it doesnt matter to me.
But you don't need a loading chute or a door for a ramp.
That wasn't the point, either. We were talking about on flat ground the difference in room needed to load the horse. You couldn't back your step up into a fence and then load your horse.
You do need flat ground for the ramp to be stable/secure/safe. With a step up you can back up to a pen, barn etc to run a horse loose into a trailer (prime example is mares with foals by their sides). You cannot do that with a ramp and not leave the opening where the horse could escape.
We have loaded our horses many times on sideways slopes, up hill/down hill slopes... No problems.
All the horse carriers (professionals) here have ramps. Just recently one of my dads bosses racehorse mares with her foal was loaded on to a conractors truck with a ramp. Yep, we backed it up to the yard, put the ramp down, and used the dividers as the barrier.
I would think it would be harder for a foal to make the step up!
I don't think you can even buy horse trucks/trailers that are step up here. Only stock trailers, and rarely are they used for horses here.