I only start to get annoyed with Singed when he starts taking multiple lanes minions.. Sure your toplane can build ZZrots and facetank the wave, but I don't think your midlaner can, but your midlaner can't push now either.. so they can't roam without losing the turret because the incoming enemy wave will have 6 full hp minions, maybe more.
I think being able to simultaneously push two or three waves is a bit much. All singed has to do is eat one wave of botlanes minions and they are suddenly pushed under their tower ready for [insert tanky meta jungle] to 4 man dive them, take first tower and first dragon.
Your mid laner can't roam down after their lane opponent, cause they don't have allied minions to stop the push in mid.
Your top laner might be able to come, but it'd require teleport and even then.. ZZ rot's can't hold forever, especially if Singed has one.
I just find his kit as a whole toxic, and I'm thankful I don't see him very often.