Testing out Song Shield vs Musketeer Shield Orb today. Against a small mob, I went from 6250 damage taken per hit to 0 damage per hit. To test the extent to which Bard Song Shield will mitigate, I went to the Wastelands with Traffic Cone, me as Bard, him as Musketeer. We took multiple smashes from the same mob. We took them with no shielding, and with Bard shielding, to find that Bard Song Shield, with my +6 Mallets, shielded a consistent 6367 damage. When we tested with Musketeer’s Shield Orb, we took 0 damage.
To test how much Shield Orb will mitigate, we went to Treesus (Bjorn, the Highsteppe World Boss), and took smashes with no shielding, and smashes with a Shield Orb from Musketeer. The Shield Orb mitigated 49,957 damage.
With Shield Orb coming up every 8 seconds, and Song Shield only coming with Crescendos (13-18 seconds average), there again appears to be a huge disparity between support there.
At this point, it’s not even worth arguing that Bard is a good choice over Musketeer. Bard is just getting shafted 
I get that Song Shield is just a Talent that you can choose not to take (in which case you get 5% damage buff to the entire party, which Musketeer’s Weakness orb can do with 100% uptime), but there’s currently no shielding abilities on Bard that are viable for end game. I’m still going to play it, but Upbeat is broken, Protection and Defense Instruments don’t work (and in PvP actually increase damage taken), Song Shield will only block the amount of damage that an overworld single mob does in one hit, the healing is less than a third of Musketeer’s, and the Ultimate is capped at once per five minutes.
Again, if anybody has any testing that shows different data, I’m more than happy to edit my statements. I just want knowledge about Bard class, and right now, the knowledge isn’t favorable for the class.