Viability of Bard Mesmerise Ability

[Hrothgaar]

To all you Bard-Veterans out there:

How viable are the Bard Mesmerise songs at higher level?
I understand that the first mez song is AoE but only works on mobs up to level 25.

All the following ones are single target so you are pretty much limited to mez just 3 enemies at a time because of song-duration, right? How viable is the mez ability with this limitation?

Also, the highest level mez songs only works on enemies up to level 54 (according to the wiki), this means that in Kunark / Velious end-game groups mez is pretty much useless? (I think I read that level 60 will be max player level then).