Darts are pretty good already and darts can already catch kodachi. If the darts can flank and cut off the kodachi's retreat, scorcher can just rush in and kill the slowed koda for free. Scorchers are faster and outrange Kodachi so they can still zone them, but it does cost a lot of micro for little damage on the Kodachi. Still though, denying that Kodachi raid is pretty powerful.
On large and open flat maps with lots of mex, koda can be pretty strong because it can pressure on many fronts and can force a lot of micro out of the rover player. But on smaller maps rovers have an advantage due to having cheap riots, and having dominatrix. Ripper is cheap so you can make a few and on a small enough map (red comet, sertalenia) you can cover most of the fronts with them and prevent kodachi from doing anything anymore. Dominatrix are more expensive, but have lots of range, and can be pretty strong against tank raiders. Usually when fighting dominatrix, at least 1 kodachi or blitz will get converted, so you need to commit hard and account for that converted unit. An army of dominatrix and rippers can be nearly impossible to assault, so on smaller maps where such an army can cover a significant amount of space, rovers are just better. And this isn't even accounting for fencer, which can also dominate kodachis on smaller maps with ripper support. While rovers do struggle more against tanks on bigger maps, its not really that big of an issue anyways. Having 1 niche where tanks are actually strong is a good thing IMO, and Rovers can still absolutely win.
Right now, darts are already pretty powerful anyways. Darts are used to fight kodachi, scorchers, and even daggers! I think they are in a good spot balance-wise.