Baby slimes do not have 200 health.
Across all core servers (Aurora, Bay, /tg/), slime health values are consistent - 150 for babies, and 200 for adults. The only difference is in damage. On Bay, water deals 1.25x damage to slime, and fire extinguisher emit far more water (but this change was made for the express purpose of improving fire extinguisher's ability to put out fire, not kill slimes). On /tg/ damages are calculated differently so it is hard for me to equivalate.
All that said, Bay's method is as usual gross overkill. Properly done, one can kill a slime with a single blast of a fire extinguisher. Buffing the damage or nerfing the health is completely unnecessary. The gross time to kill a slime with a fire extinguisher is twelve seconds, so one might simply consider buffing the metabolization rate just to make it less of a length process, if anything.