Yeah, his negative impact on team versatility would probably more than negate any hypothetical offensive upgrade against LHP.
Valencia's career wRC+ against lefties is much higher too.
The only value that Tank really carries is upside value. He has bat speed, easy plus power (double plus raw?), and true spray power to all fields. (chart)
At his current skill and projection, he's a liability. He'd have to figure something out to be an asset, but at least some of the tools are such that he's "one click" away from being a guy you'd want on the team.