My reasoning is mostly based on the diagrams present on Railway_stations recommending ref=1;2 for railway "islands" that are in the middle of train tracks, and the general principle of "One feature, One OSM Element"

Splitting the platforms creates an ambiguity around their physical reality: are these physically separated platforms (e.g. with a wall) that should be treated and routed to differently? or are these "logically" separated platforms that are still physically the "same" platform?. Whereas having them as a single area with `ref=1;2;etc` clearly indicates that "This is a mapping of a single physical platform that has two platforms on it", even if it creates an ambiguity around where specifically those platforms are. I think Kovposch comment on the `platform_edge` talkpage under "More hassle than it's worth" generally summarises my thoughts as well. 

As for platforms 4 & 5, I noticed it, and plan to fix it sooner rather than later... but relations are a pain to deal with 🥲