The only way Nash can really capitalize and dominate Ken in the match-up is to establish a finely spaced fireball game and even then he has to be ballsy with where he throws plasma, Ken’s work around options aren’t strong enough to properly fight against some strong fireball pressure with the occasional Moonsault to get in. But people do seem to forget Nash can’t actually retaliate from knockdowns and we have some great ways to set up oki, all it takes is one counter poke to carry the entire round, or at least force Nash into a corner. Trying to play a footsie game against Nash won’t get you far, and giving Nash the space to freely throw fireballs and threaten things like Moonsault/dash - throw is only gonna get you bodied, I recommend the Chris T approach - rushdown, and rushdown a lot. Force the corner through a counter poke or a hit confirm, and get to work on your pressure - lows/throws/overheads/shimmies. You have the tools to make Nash second guess himself again and again, remember he doesn’t have a reversal option so his defence has to be on point, capitalize on this and go HAM when given opportunity. You can also stop most of his annoying pokes, at least somewhat. You have a counter-poke to each of his step kicks and the bazooka knee, use st.lp to stuff the bazooka knee, you can try to use it for the other two step kicks but it won’t be as effective as it’s a lot less lenient. You can use st.mp to stuff both of his step kicks, just get a read and throw it out now and again to scare him away from using those moves, it should give you the edge you need in the neutral to close the gap. Moonsault is NOT an issue vs. Ken, MP DP and cr.hp both beat it cleanly, if he sets up the Moonsault behind a fireball just neutral jump mp/hp depending on where he is in the arc.
Not as bad as Chun or Vega, nowhere near as bad as Necalli. I’d probably call it a 5-5, Nash doesn’t really shine against Ken.