Thats not true. Perhaps some people don't notice the lag and frame rate hiccups but if you change often between PS4 and remote play the difference is very noticeable and annoying even in slow games.
Digital foundry:
http://www.eurogamer.net/articles/digitalfoundry-vs-vita-remote-play
http://www.eurogamer.net/articles/digitalfoundry-2016-hands-on-with-ps4-remote-play-on-pc
Summary:
"Games are not unplayable by any means but you will feel the difference. If you play competitive games, such as Street Fighter 5, you may struggle to perform at your best under these conditions."
Again, I'm not saying there's no lag, but saying that remote play is
only good for "very slow" games downright false.
Also, I can't speak for remote play on PC (which relies on network, while Vita also has the benefit of connecting directly), but the first article about Vita is from 2013, and Remote Play has improved a lot since then: back then Vita couldn't even accept a 60fps stream.
Dismissing the technology as a failed experiment is baffling honestly, there's lots of fun to be had with remote play, even in frantic games (remote play resogun at 60fps is quite enjoyable, for instance), and I'm sure many people on this board can tell you that. Sensitivity to lag issues is also quite personal, provided latency doesn't reach crazy high figures anyone would notice.