Roaming is actually a pretty important skill for a support to have and should be done no matter the skill level of the adc. However, during laning phase at the very least, roaming doesn't mean never be bot. Even for a bad adc, it's good to still show up in lane. A lot of players don't know how to play laning phase 1v2 so leaving them for good during laning phase can lead to things snowballing worse and losing dragons/bot tower/etc while the adc gets no farm or xp.
One of the most important thing about support (and most roles I've found) is that sometimes you have to adapt to the playstyle of your team. If your adc doesn't follow you when you try to engage, then stop engaging when it's just you and your adc. On a similar note, if your adc gets caught out trying to 1v3 and you don't think you can save them, it's absolutely fine to ditch them so you can survive.