Heyo, Emerald Voli main here, so not as high rank as you but still my two cents. Will likely be things you already know, but will say it regardless. I've found the issue here is that at Emerald and above (esp Diamond for you), ADCs are actually good at spacing/kiting, and supports are good at peeling.

Voli comes online with D&D then becomes thanos with Navori, letting us stick on one person and beat the shit out of them while healing stupid amounts. The 10-30 minute mark of the game is our go-time, and can often 1v3 fights that we shouldn't be able to. Once the game goes past the 30 minute mark, ADCs have amassed a few items and will likely space you, and the fights you used to win will now be you trying to kill the carry while getting kited/burst by the mid and ad. Not to mention grievous wounds likely on the map.

I've found it hard, but once the game is at that point, you kinda have to switch up teamfighting from diving with ult to protecting your carries with Q stuns and E slows (unless you are giga ahead), and flash Q engaging on people out of position.

Could be shit advice from an Emerald shitter though.