1) You assume the market cap or weightage assigned for each company to derive the ASPI is equal for every company and that every company will be equally affected. = This is because you have applied 18% on the ASPI instead of the ASPI's components.
2) You assume that the every company is subject to the effects of the super gains tax. = This is because you have applied 18% on the ASPI instead of the ASPI's components.
3) You assume all industry PERs average to 20 (or 10). Using an average with high statistical outliers will produce unreliable results. = This is because you use a PER of 20 (or 10) in your calculations.
4) You fail to take account of the one-time tax policy reasoning.
5) You do not factor in the ability of companies to increase their leverage in order to pay lower tax amounts (as the tax is bottom line based and not top line based).
6) You assume prices will reduce proportionately to earnings. This is because you multiply the tax amount by the PER to calculate the loss in market capitalization.
I hope you don't see this as me criticizing your formula. It's almost impossible to factor in the assumptions that you've made.
I do however believe, it is important that you MENTION these assumptions before attempting to scare the entire forum.
And with that, PLEASE INVEST ON VALUE AND NOT SPECULATIVELY.