You still have to ave x number of feet for the horse to face up to the trailer with no ramp... I would venture to say with my float, (ramp) I would only need 1 or 2 more foot of room than if I didn't have a ramp. That's not enough to worry me.
Our ramp is covered in rubber with string in it (so it is rough) and it also has ridges every so often down it, horizontally. I've never had a horse slip on it, even in heavy rain.
Our ramp is light enough for me (19yo girl) to raise and lower myself.
My concerns with a step up... For me, it creates more danger. If I have a horse who rushes on or off a float, then a ramp allows them to do so safely. A step up can either cause them to fall, or launch out of it dragging me by the lead rope :] lol. Sure, I will teach the horse NOT to do so, but i'd rather be safer in those intervening times when it is still learning.
Also, teaching a horse to load... With a ramp, you can go a step at a time. The horse can stand half in and half out and get used to things, think about things, etc... I would think standing half in/half out of a step up would be uncomfortable and not very productive... Also you can't do it in steps. They have to jump up the step AND enter the big scary cave at the same time.
I will always have ramps, our current 2 horse straight load has one, our soon to be owned three horse angle load has one, and if we ever get a truck, it will have one. I just think it is way safer for me, and the horse.