Yah mobile meowth sucks, the worst part is that it can spawn disruptions along your coin lines too.Poisonous Mist activates more often than Vitality Drain. It activates 15% of the time on 3-matches, 25% on 4, and 30% on 5. With Vitality Drain, it's 5%/10%/30%.
I find that I average 300-400 on Meowth (on 3DS), going for 5 coins most times. It's much harder on mobile, with the RNG determining whether coins or blocks spawn.
Also surprised that poisonus mist has a decent activation rate, it's similar to vitality drain's on mobile iirc.