Decided to take a visit back to this site and I can explain this one. First of all, the only relevant mini in the meta is the vanilla one with missiles. I'll start with the main weapon though. First of all, this thing is a paint machine. It's output is so insane which makes it great at supporting other players (to the point where it can help make blasters viable). It has good range, deletes things with object shredder, in general is a god at supporting players while being untouchable itself (which is what any midline should strive to do). The reason the other variants are kinda irrelevant in the meta is because for zimi, curlings suck for the role the mini plays (and curlings are not great in general). Rain is a good special but curlings don't do anything and missiles are a more viable pick (will get into this later). Kimi doesn't get much worth from it's kit as a midline either. You can play it as a front but there are more powerful options.
Now I'll explain why people actually use missiles (to the point where kshot and vimi are meta). This one has been pretty weird to see to be honest. Literally just all of a sudden with no patches or anything missiles were seeing use. It started with people experimenting them on small maps like MakoMart where they became a niche pick, and in this process people saw their potential and how they can use them not only for tracking but for paint and pressure. There's also some crazy special pairing like missiles + stingray which applies tons of pressure that you only need those two, and your other 2 players can save their own specials for a longer, stronger push.
One more point I want to make is that the scene is developing to create separate mode metas in terms of weapon comps. For instance, vimi and other painters like h3d, explosh, remix, etc are super strong in zones, but weak in other modes. Inkbrush nouveau is a top pick in clams and turf but isn't great otherwise. Stingray is a requirement in tc/rm but doesn't need to be run in other modes. Vimi fits into that zones meta but isn't always the best pick for every map/mode. Basically my point is that the meta no longer encapsulates using the same comp every map/mode like early in the game, but abusing the properties of every map/mode which let more weapons see use.