Remember, your blade song ends if the enemies grab you and force you to don a shield.
You sure you want to dump strength?
Um... nobody can force you to don a shield outside of
domination,
suggestion or similar magic as it requires an action from YOU. While you can assist someone to don armor, there is nothing in the rules that states you can force someone to don a shield.
In fact, based on the way the rules are written overall - as a general rule, a creatures equipment cannot be targeted by spells/abilities/effects unless explicitly stated by another rule. This is due to the fact that most spells/abilities specifically exclude equipment.
Even things like disarming are difficult in 5e, as it either requires 3 levels of
Battlemaster and a specific maneuver (
disarming strike), or requires the use of an optional rule from the DMG which only applies if the DM uses such a rule. If disarming a target is that difficult, why do you think it would be
easiier to force a creature to equip something? That would be several orders of magnitude more difficult than disarming them.
Then there is the fact that a literal reading of the rules states that the blademasters ability ends when they
Use a shield. This requires deliberate intent. Even if we say that by some unknown method you can force them to equip the shield, you cannot make them
use it. This may have the result of forcing them to spend their action to doff the shield, but that is about it.