While I don't use jackramps (honestly I don't know how), I think they're great.
First, it's one of the few things that can actually get through the porc slag heap that is the front line in big teams.
Second, it showcases the sandbox and modular design philosophies of ZK in a semi-competitive setting. You literally build your own superweapon from component parts.
Finally, it punishes people for not making any units - while 99% of big teams punishes anything remotely mobile for not being high enough weight.
So long as people are using them effectively (not rushing it in a 2v2 for instance) I don't really see any issues.