I agree with you. But I assume that the Imp's role in a zombies team is to infiltrate the plants defenses and "unroot" pesky peashooters/sunflowers using Gravity Grenade. I forgot if he can prevent Chompers from burrowing or not. He can also counter Cactus at close range (without gravity grenade) as she will panic and have it hard to shoot you at close range.
Other than that, the gravity grenade can be used around corners while you take a distance to avoid fung fu or other abilities like chili beans or peashooters' normal peas, that is to stop certain players from chasing you after sustaining heavy damage.
But all-in-all, Imp's abilities are underwhelming in general (straight out of the box with no upgrades) unlike other heroes like Nightcap who have it really easy and everything seems buffed with no upgrades required.
They should increase the gravity grenade radius a bit or increase its duration. While also giving it other effects, like suppressing Fung Fu (She's only do it inside the grenade radius) or eating up a chilli bean blast (compressing it inside). It should also suck all Acorns above Oaks if an Oak passed by it. This way, the Gravity Grenade would have a better purpose than just floating enemies for few seconds.
There is another problem though. I think that his Impkata doesn't combo well with the current Gravity Grenade. If enemies can shoot you at free will while using abilities after getting caught in a Gravity Grenade, then you just die quickly with your 75 HP as you try to get closer to use it.
I suggested Highlighting Ally Players previously so that I can use my Gravity Grenade around Super Brainz, All-Star, Space Cadet and other players that I think I can combo well with. That would maximize the benefits of gravity grenade. Rather than just throw it without knowing who's around me exactly and have its duration run out without any benefit.
Imagine using it while a Space Cadet use her Gravity Smash or Crater Maker to erase all gathering plants. That would be game changing!
