Honestly, GL will always have a hard time being a mechanic so long as it's tied to any form of DPS increase, especially one that stacks up.

We see this with NIN, DRG and BLM where their maintenance "Mechanics" are non-interactive. Where you press a button to toggle it on and then you forget about it while you fight unless there happens to be a long transition phase (With the exception of NIN occasionally using a second finisher for their filler combo to refresh the duration)

If GL is tied to any form of DPS boost, then any kind of interaction that makes you concerned with spending it, will end up being mathed out if it's actually worth dropping that DPS buff for the use of the skill (Which tends to only be the case in times where actually stacking GL is trivial, i.e. StB with multi-Shoulder Tackle giving GL stacks)

As far as speed manipulation goes, it's a universally hated mechanic. Not only have Monks been vocal about how awful it is, but back when AST had cards, people often expressed distaste over receiving The Arrow because of how the shift in speed would mess with their rotations. Well, this is speed manipulation in combat.
One could propose a rework to the "Fists" that would enable people to select a speed of MNK they find the most comfortable. I.e. Earth is slow, Fire is medium and Wind is fast. With of course, the slower stances gaining increased %damage to compensate and make all 3 equal for DPS. This would also help alleviate the concern the devs have over the 4th GL stack and MNK becoming "Too fast" and having a rift between good and bad players widen since the bad players that cannot handle the high speed can instead opt for a lower speed that suits them.

If then, GL's speed and damage was then tied to Fist stances, there would be more flexibility in having GL be an actual resource, with the ability to spend it without having it compete with the raw damage gain you lose out on by having to restack it. Heck, you could even have GL stacks interact with Chakra too, something like "Gaining a GL stack while at max GL instead opens a Chakra" which would also open some more flexibility with Perfect Balance allowing it to be used to generate several Chakra quickly, in addition to adding in the thought process of whether you want to hold onto your GL stacks and generate guaranteed Chakra or if you want to spend them for TK and rely on just crits to generate Chakra while you build stacks back up (Which would likely be beneficial during periods of having crit buffs).

Though, if you wanted to keep GL stacks offering a passive benefit, you could use alternate stats aside from SkS or raw damage such as Crit chance (If Chakra is still reliant on crits...), heck, maybe even some inverse scaling where for example, at full GL you get guaranteed Chakra from executing Coeurl Form skills, but don't get any from random crits. While stacks take you from a 100% chance on weaponskill crit (0 stacks), 75% chance on weaponskill crit (1 stack), 50% chance on weaponskill crit (2 stacks) and 25% chance on weaponskill crit (3 stacks) before hitting the 4th and final stack.

In addition to this, you could also tweak Tornado Kick to where it's usable at any level of GL, but its damage scales up with each stack. So one can maintain low stacks if they wish to try and captialize on Crit buffs *Cough*Bring back Internal Release*Cough*