Again, Tenka-goken is a cast, so (unless you're using tsubame which is only available every 1 minute (besides during the opener or re-opener)) you're not able to move back and forth between conal and circular AOE ranges to accomodate for the placement of the AOE as easily. Because Tenka Goken is a cast, you can't easily move forward again from conal AOE distance into the enemy group to resume your circular AOE combos unless you perfectly slidecast or have a tsubame in store without delaying the next Fuko GCD to get the best reach. Keep note that even with a slidecast, the slidecast window isn't very large and looking back at the diagram above comparing conal and circular AOE range and distance, the distance to travel will most likely be quite huge, huge enough to cause GCD delay.

There are definitely strong benefits to having Fuko such as the fact that for most part of the rotation preceding Tenka-goken there is barely any movement transition involved since Fuko and the combo GCDs (Oka and Mangetsu) are all circular AOEs, but moving between conal and circular AOE positioning with Fuga (even if it involves more movement compared to Fuko), these GCDs are not casts so there is enough time to move between positions for the next GCD, but the same unfortunately may not be said for the transition between Tenka Goken and Fuko, which provides a huge risk of GCD delay - a concept most players are encouraged to avoid to perform well in this game.

To finalise, many players may enjoy the changes Fuko brings to the AOE rotation, and some of course feel strongly opposed. Fuko definitely brings more damage over time due to the increase in kenki gain and the small potency increase, and some may regard that as the justification for all that went wrong with the telegraph change, but the inconsistency with syncing and the GCD delay risk may make it feel like it was one of the lesser useful or overlooked developer decisions made over job changes for this expansion. Also, considering the fact that this is one of the only abilities in the game that had its telegraph altered upon leveling up, I for one definitely disagree with this change, and do hope that the developers realise this and consider making some sort of alterations (although that is definitely a longshot).

Thank you for reading. This was written during the early days of Endwalker in patch 6.01.