While the idea of a stance system is interesting in concept for our magical fencer, I have to question this particular skill for us on the grounds of practicality.
We don't need a skill to turn our melee combo into an AoE combo. We already have Moulinet for AoE. If we had an AoE melee combo that ignores Moulinet, we would ignore Moulinet full-stop.
Without Contre Sixte providing an alternative enhancement option to the combo, we'd just have Fleche adding flat damage to each melee action, which essentially makes it a waste of a skill since the devs would just reduce the individual melee actions' potency to compensate for it. And when you factor in Manafication bypassing the 40 second wait between combos, and the combo acceleration we get each expansion from things like Scorch, we wouldn't necessarily have either one of these skills every time either.
Plus it would mean losing oGCDs from between our slidecasts, which just seems like a huge waste of all that extra time.
I do think it's an interesting idea, but definitely not one for RDM. Maybe for another melee job.
I can agree with the sentiment, albeit not the specifics. RDM's kit is solid, functional, and doesn't have any glaring mechanical absences like some other jobs. It could be treated as holistic, which I think any job should kinda feel like at level cap for a given expansion.
I do, however, believe there is still room for additional expansion to the kit -- that it's a strong foundation that can be built off of, not necessarily the best it will ever be. Like how BLM felt "whole" last expansion with Foul as a capstone, but still had little spaces to slide into here and there without overcomplicating it this expansion.
In RDM's case, just to pick at a few plausible (but not strictly "necessary") openings: expanding Moulinet into a combo (or pseudo-combo), dual-Mana procs or oGCDs to accelerate the main combo without imbalance, or virtually any spell that could fit into our Shortcast-Longcast casting model. All that without having to add a second gauge (and we're one of the few jobs that doesn't have one, or any timers like DoTs or sustained buffs).
I also believe some of its issues aren't strictly related to potencies and would be better addressed via alterations to its existing mechanics. You have to know that the "Raise Tax" won't go away (if it ever does) without adjusting our relationship to Verraise.