I think the PLF is a good thing, for several reasons. Not sure what else could be used. Most of the Parkour type falls are simply modified PLFs, at least from what I've seen on the videos.
First off, the forward speed one sees on landing usually isn't all that high (swooping excepted). If the landing is anything approaching normal, forward speed should be mostly bled off by the time the ground is met.
A more or less standard PLF is perfectly adequate for a fair amount of forward speed. You just roll forward more (further). I've turned running landings into PLF/forward rolls when I found that I couldn't move my legs fast enough to keep up with my body.
Slides have their place, when properly executed. I've adopted/adapted something resembling a baseball style slide. I start it while the canopy is still supporting my weight, and just sort of settle down on the side of my leg and my hip as it progresses.
One problem with this is it needs smooth grass. If I'm not certain there aren't any holes or ruts, then I roll it out. I had one where I saw a nasty rut from the lawn mower tractor (probably 5" deep and at least 8" wide) that would have easily caught & injured my ankle. I abandoned the slide idea at the last second & rolled it out.
Another problem is that it has to be done correctly. Tandems often slide in, landing straight on the butt. For a landing that is smooth & properly flared, this is ok. For anything else, it can cause spinal injuries. "Unteaching" students who want to do that can be challenging.