Troll?Latitwins hit harder, have many more niches such as defog, a speed tier decent enough to speed tie some of the faster threats, recovery, and nice coverage. If you want to run a sub+CM keldeo latias is around the corner with better speed and recovery. The only thing keldeo has over the latitwins is dark resistance meaning no pursuit trapping, and before greninja was banned.. keldeo was effective at coming in on it with scarf, killing greninja or nailing a switch in with a super strong STAB move. Without greninja keldeo doesn't have as much use over the eons outside typing syngery with certain teams. He doesn't switch into much outside of greninjas who foregoed extrasensory in this meta and that's exactly what was removed.. turning keldeo into more of a momentum killer/dead weight depending on team match up.
Well, you don't really seem to get it, keldeo being less effective against without greninja?? Might apply for scarf, but that's really not its only set. Sub cm eon with recovery? Because mono dragon or mono psychic is so good, the only thing actually runing us cm is mega Latias.
Outside of type synergy? Well how the would two special attackers difference themselves outside of that? Keldeo have different stab moves, different resist, the only thing the two share is being special attackers. And two more points in speed is not enough to ever use the Latis as replacement for keld.
Keldeo is a nice check to bisharp, tyranitar and m gyara, Latis gets eaten by those. Keldeo is great against sand, lati is not. Keldeo and Latis are so freaking different I can't help laugh at someone comparing them the way you do! I could explain it in a lot more details, but I find it laughable that it is even necessary.
Also, while you might not consider keld for S, it is still one of the stronger A+ mons, you basically treat it as if whas something gimmicky nominated to D rank for its ability to check greninja.