Definitely agree. There were plenty of ways of handling it that didn't involve doubling Ikishoten's cooldown. They could have tied it to Guren/Senei instead, tbh, and it would have the exact same usage pattern as now, without requiring Ikishoten to be 120s. In fact, I'm a bit astonished they didn't attach it to Guren/Senei, it seems like an obvious target for it.
They could instead make it work like Life of the Dragon, where each usage of Ikishoten or Tsubame granted a stack. Downside is that it wouldn't be available on the pull (and in fact, would desync, because you'd get the 2nd stack at the 60s mark), but they could fix that by having either the first usage in a given combat session grant 2 stacks, or have an ability like Reaper's Soulsow that's only realistically usable outside of combat and grants a stack, so the first usage would bump it to 2 stacks and thus allow usage.
Personally, I'd prefer just tying it to Guren/Senei instead, though.
Personally, I think Samurai could use a charge-based or resource-consuming GCD attack, similar to Sabre Dance for Dancers, which serves a very valuable role for aligning GCDs prior to Flourish. In the case of Samurai, it should probably be designed as something that's essentially a null DPS gain/loss, so it can be used or not used as needed.The filler GCDs in the rotation are a known annoyance. We don't know if that is going away either. I'm going to be pretty annoyed if I have to use Yaten>Enpi to maintain CD timers (I don't like using movement abilities for filler or a DPS increase at all). I use Yaki filler right now, and it's just meh as well. I really hope that was on their radar and this stuff aims to mitigate that.
If they added a new on GCD melee that did ~500 potency and cost 10 Kenki, it would land at the same potency as Yaten + Enhanced Enpi + Gyoten, and the same cost, without requiring the movement, and fill a similar role, delaying the GCD sequence to align better. Or alternatively, closer to ~370 potency (based on the potencies in the EW tooltips) and not have it cost Kenki. Maybe drop the potency slightly from a "null" potency level, so using it is a small potency loss, made back up by allowing the burst sequence to properly align, to prevent that new ability from simply being spammed (could also give it charges to help prevent that, though with a relatively short CD so it's generally readily available for its intended GCD-alignment purpose).