No i did nothing wrong. It also had nothing to do with kill order. it has everything to do with enemy never stopping healing. My bad for going to the town at a reasonable pace without arbitrarily grinding the same dumb mobs over and over again to level up bots so they can out-dps an infinity loop heal

Did you use the apolonia? as she mow down the plant gym at lvl 4 just keep her mana up and spamm guided missiles. then take out the bots that attack and leave lily bot for last as she tends to only heal herself.
I first went after clemati as she is squishy and can be defeated fast then mantis as she can heal & attack, after that I took out the last attacking bot then finally take out lily.
The reason why I did it this way is that I found out that lily is bulky and I took her down to 1 hp and missed an attack and she nearly fully heal herself. I also found out that lily rarely heals the other bots.
edit: granted I did only have 3 bots with me when I did this.