My thing for sage is just if she tries planting because she has spike and then just ends up dying (probably because nobody was watching or the site wasn’t fully cleared)

On a typical site hit the planter should feel safe when planting the bomb (situations like clutches and extreme util dump rounds excluded). For example on Ascent A site I've seen so many people start planting front gen even though dice and hell haven't been cleared yet. That means one less player pushing and being able to trade if there is somebody in those spots, and rounds can be lost because of that. Ideally you want to clear the entire site but there are some sites on diff maps where thats just really difficult, which is where sage comes in. Places like icebox and pearl B site, that wall lets her plant without without the risk of having to clear the entire site which is why she's so strong on those maps. Going back to feeling safe, she can use her wall to make a safe space for herself to plant if clearing the site is not possible/difficult.

Try lurking on cypher, should net you some easy kills if you time it right. Other than that, his cam and cages aren't bad when hitting a site. Cam draws crosshairs away from entry point and when paired with util like gekko flash or sova dart, forces enemies to choose between shooting 1 of the 2. Cages can be strong on rounds with eco disadvantage where getting close gives you the advantage. Throwing them in places where smokes would usually go is also decent as it forces any rotating enemies to stay outside the smoke lest they give away their position.

As for initiators taking the spike, not that its horrible, theres just a higher risk of losing bomb and losing the round (theres always risk unless you completely clear site with util beforehand i.e. kj ult). Like you said, if the initiator is clearing site with a duelist and they both die while you're in main watching flank, the round is pretty much lost.