From my experience, most of what you see out there regarding what a particular species needs, are only recommendations at best. And sometimes information is misleading, if not outright incorrect. Most freshwater tropicals don't 'need' sand AFAIK, although some may prefer it or need it for spawning, which is a different story entirely.
Another factor leading to confusion is that IMO, ichthyologists or other sorts of academics who write about fish, often advise keeping a fish in the state they found/studied it in the wild. But many popular fish among aquarists - including rams, platys, and certain corys - are bred in captivity, under very different conditions than they are found in the wild. Nevertheless, they thrive, because like most organisms, fish can adopt to changing conditions, provided things don't change suddenly.
Also seems that many writers and websites sometimes advise keeping a particular fish under particular conditions because they can do so and have done so with success: They have the space, the funds and the dedication required to maintain numerous tanks, each maintained in the optimal conditions for that species.
But for 'regular folks' it's not necessary to provide optimal conditions for every particular species. As long as you stick to common, hardy species, and keep your basic water parameters within bounds, you can achieve much success and maintain a beautiful and healthy aquarium without 'sweating the small stuff'.
FWIW I have kept quite a few rams with success - always with plain old riverbed gravel, in fairly hard water which is slightly alkaline.
Rams and corys are hardy fish - they should be fine, provided you don't overfeed or overcrowd them (much more important than fretting over the fine points of substrates), and ensure that your water temperature, ph, ammonia and nitrite levels are within acceptable bounds. (overfeeding or overcrowding kill fish to a large extent because those things mess up your water quality).
Platys are reputedly hardy, but in my experience they are not particularly so. YMMV.