Of note is Armor of Agathys for the Bladelock. In my Tomb of Annihilation game, our bladelock uses this spell (only able to cast 2 spells at 5th level, which is often Armor of Agathys and Hex or Hellish Rebuke depending on the situation) to devastating effect when fighting mobs with either multi-attack or multiple mobs. With 15 temps and inflicting 15 damage each time he's hit (until the temps are gone), he's a pretty effective martyr build.
Additionally, the effectiveness of a Valor Bard, Bladelock, or Bladesinger is highly dependent upon the party makeup. My Tomb group has a remarkable amount of synergy; they have a diviner, a bladelock and a grave cleric. The group is fond of taking those diviner portents (especially if there is a 20) and handing that to the bladelock, who then powers up with Hex+greatsword+Cha. The grave cleric then uses her channel divinity to grant a single mob vulnerability to the attack, and the bladelock goes to town.
Bladesingers are difficult to hit...I had one in another game. Especially at high levels. However, if you can hit them or use spells against them (target their weakness...usually it will be Con), then good damage will take them out.