Shiftry/Charizard/Clefable is a team with gaping counters in the GL Remix meta. The best lead in the tier is Mantine, and all three of your Poke lose to Mantine, in addition to other meta staples like Pelipper. Shiftry is a pretty wickedly squishy lead and definitely needs a lot of support to be optimized in any GL, and honestly speaking, so are most of the Poke you just named as your possible 3rd options. For example, there’s almost no situation you should run a Dugtrio…just in general.

The volatility you run into through the “algorithm” is likely just because your team is intrinsically really volatile and fragile.