If there is nothing to weave, then don't clip your GCD with Ruin 2, and simply just cast your next Broil. Your ping really shouldn't dictate your CoA here, unless it's absolutely atrocious. It's kind of one of those things where you can actually feel your DPS drop when you do it. If the situation calls for a support ogcd such as a fairy skill, you can sub that in and you can consider the pot from Ruin 2 as free damage for using a support ability.

There are some cases where GCD clipping is ok. One example I can think of is when a boss is about to transition, or any time you want/need an additional 200pot tacked on very quickly, because you can't actually clip a GCD if there is no target to use one on. Also understand that while it is good practice to avoid clipping GCDs in any content, try not to beat yourself up over it too much, especially as the healer role. Playing this role optimally entails evaluating the situation for every action you use. There is a checklist that a healer will go through before finally arriving at 'smash DPS button', and it all takes place in the 2.5s GCD window. That is why they don't have a true rotation. I'm not downplaying min/maxing, but just be mindful if the situation calls for more DPS uptime, or more healer awareness.