Have You considered different field shapes, slopes for the ball to roll on etc.? The biggest issue right now seems to be the field itself, as Lucio is all about that wallride, while the field is designed with complete lack of any consideration for the wallride.
Just dividding the field into the middle field and two side “terraces” ending with slopes towards the goals would ad both verticality and additional walls for the wallride. At the same time the jump pads would start to make much more sense.
Also one more thing would be a MASSIVE help - have two indicators on the screen to show if the ball is in range of abilities. Two icons with a fist and boop that turn red when the ball is to far away to be hit and green when in range. Absolutely simple and reliable solution for one of the biggest issues of the mode (or, just add an “aura” indicator of range that looks like the AOE range indicators in regular games).