Bladesingers got a lot of great goodies in Xanathar's. They didn't receive much if all you care about is melee Megadamage. But I have to say, I'm not particularly sympathetic to that complaint. Not counting EEPC spells, Bladesingers now get Dragon's Breath, Enemies Abound, Thunder Step, Tiny Servant, Charm Monster, Danse Macabre, Steel Wind Strike, Mental Prison, Scatter, Soul Cage, and Illusory Dragon. That's PLENTY of additional power, so long as you don't restrict the definition of 'power' to 'boring melee DPR'.