Didn't watch the video, but that is KY Dam Marina. The ramp is actually too shallow at winter pool and even bass boat trailers will drop off the end. You'd think they would try to get it right when putting in a new ramp, but I guess not. The courtesy dock is on ground at winter pool too
We did a slide in ramp on Monroe at Fourwinds (the IDNR one on the point) about 10 years or so ago. We used two D9's and cast and pushed 3 sections, connecting each new section to the above water section of the previous one. Worked like a charm.
Even with a ramp that wide I would still guess there'd be a few guys that would still back in their truck/trailer so crooked that they'd take up the whole ramp.