Not OP.
Toxic Citron is quiet weak in a 1v1, but incredibly annoying and effective when bombarding groups.
I am actually surprised that so many people troll with E. Citron, but almost no one ever plays T. Citron.
In my book T. Citron is an excellent "Suppressive Fire" character, that makes people run from areas. So multiple of them can deny you basically every spot on the map.
I agree he is not OP, though just as you described, a really good player or multiples can really make a game frustrating, . Try him out on a boss hunt or crazy ops and you'll discover that his DPS is somewhat lacking. I mastered him easily in ops, but I've never done well with him in multiplayer. But then I've never been much good with characters who should keep out of the way and support from a distance. Same with characters like alien flower and rec'rose. I seem to lack the self discipline and/or positioning skill.
Classic statement by @dwooten77, I've been using the Park Ranger often too with heavy hit rocket to break up the charade...
