I agree with all of your post, except the merit of LO Air Slash is not applicable, as the primary set uses Psychic, which is:Sorry I dodn't have time to update; been busy lately. As jrrrrr said, there's no need for a full-blown debate here. I finally did some calcs to compare LO and SubPetaya, and here they are.
These calcs deal with the Pokemon that might want to switch into Yanmega (barring Chansey, who cannot be dealt with without Reversal):
SubPetaya HP Ground vs. 252 HP / 168 SpD Registeel - 37.36% - 43.96% (clean 3HKO)
LO HP Ground vs. 252 HP / 168 SpD Registeel - 32.69% - 38.46% (negligible difference)
SubPetaya HP Ground vs. 252 HP / 220 SpD Regirock - 47.80% - 56.32% (high 2HKO chance)
LO HP Ground vs. 252 HP / 220 SpD Regirock - 41.76% - 49.18% (falls just short of a 2HKO)
SubPetaya HP Ground vs. max HP / max SpD Steelix - 62.43% - 73.45% (easy win)
LO HP Ground vs. max HP / max SpD Steelix - 54.52% - 64.12% (no real difference)
SubPetaya Air Slash vs. 168 HP Crobat - 64.02% - 75.35% (slight chance of OHKO w/ Stealth Rock damage)
LO Air Slash vs. 168 HP Crobat - 55.81% - 65.72% (significant difference)
SubPetaya Air Slash vs. 4 HP Crobat - 72.44% - 85.26% (very high chance of OHKO w/ Stealth Rock damage)
LO Air Slash vs. 4 HP Crobat - 63.14% - 74.36% (just misses the OHKO mark)
Both sets have their merit. SubPetaya edges out LO when it comes to Crobat, and manages to beat out Regirock as well. However, this is at the price of multiple turns of setup. The LO set can come in and hit hard right off the bat; while missing out on a few KOs. However, their playstyle is very different and, thus, they both deserve their own sets.
I'll probably change the name to Substitute, but write the other items in a different paragraph, not slash them in.
LO Psychic vs Crobat: 97.33% - 114.54%
So the LO Yanmega has an advantage over the SubPetaya one pertaining to Crobat, not vice versa as you suggest.
However, the LO variant cannot 2HKO Registeel most of the time with HP Ground after Spikes + SR, among other things. You should have mentioned that ^_^. The SubPetaya set still has various advantages damage wise.
And I agree with your plan as well.
EDIT:
I just did the Modest LO Psychic vs 104 HP Crobat. Its 97.33% - 114.54%, so not "no matter what", but most of the time.LO should have Psychic, which OHKOs Crobat with Modest LO no matter what. Slash them in because they're viable and arguably better.
And, "them" could mean alot of things...can you clarify please before I argue the wrong thing lol?