WIND
top cc suggestion, is make bard mez duration scale if they have a wind instrument equipped in some form.
this would now be at major cost of their buff effectiveness for not having a 50-100% lute out, esp now the song baseline values are reduced down.
that is "fine" as a decision cost.
if the full 50-100% instrument scaling is too large as raw duration (27-36s so probably would be), scale this against say a flat 6 second increase from 100% cap
e.g. a 50% vendor instrument boosts mez duration by 3 seconds from base 18s to 21s duration
e.g. a 100% bis instrument boosts mez duration by 6 seconds from base 18s to 24s duration
the other interesting option this could then give is for it to interact with the new cooldown power
Crescendo - Raise your song in a mighty crescendo, increasing your Instrument bonus with all Instruments, as well as Singing.
(tooltip of this power states it gives 50% instrument bonus for 30 seconds, cooldown unknown)
if during this power it then gave an additional flat amount of increase to the mez duration in seconds
e.g. 50% vendor instruction gets another 3 seconds for 24s duration
e.g. 100% bis instrument gets another 6 seconds for 30s duration
at the moment it looks like the only wind instrument scaling is the AC/Absorb song, which does not even unlock very late in the 30s level and has extremly low values and frankly does not compete with the values you get from a lute's HP regen let along the other lute songs such as mana.
* i can only assume that is the wind scaling song from it's name "Faedawyn's Piping of Protection" the vendor tooltip preview does not tell you

5 L34, to 45 L60
so 7.5-10 L34 to 67.5-90 L60 values with 50-100% instrument
[this song could use something more like increased to dodge skill etc]
lute is still king for in combat instrument choice.