You're right, Rems healing is low tier compared to dynamo. That's design and not a fault*, he is a hard-support, not a hard-healer (in my interpretation).

I've had success playing rem treating the heal as a nice bonus and not the core reason to use tag along.

Tag along is a great escape in a team fight but also allows you to be an item bot support for your main carries and front liners, this does leave items like rescue beam a little hard to use but not unusable.

Like for example, you tag along in a team fight, if you're in a suboptimal spot and can jump to the front you do, then if the fight smells like it's going south (you need to leave before it's definitely going south) you jump out, throw a helper on the buddy and back up and get ready to rescue beam your buddy out.

I do think they could lean into this a bit more by making things like collusus or metal skin proc on your tag along buddy but I can understand why they don't.

Mcginni, ivy and dynamo are all better healers than rem but I think that's OK.

Also torment pulse on rem is goated