Since I see that now the 210 gigaton calc has been accepted for Luffy, how would this affect the lower Gears which backscale from this?
Because the
scaling page right here says at the very top that Gear 4 is 9/16 of his Strongest Attacks (and it makes next to no sense for Gear 4 to be just 1.1 gigatons when his Strongest Attack is now almost 200x that, otherwise he would've just used his strongest attacks to one-shot Cracker and Katakuri from the get-go since it's so far above High 7-A), putting it at about 118.195 gigatons.
Also, I found a much better way to downscale Gear 2nd + Busoshoku Haki from Gear 4, since we know that Gear 2nd + Busoshoku could barely break one string, putting it at no more than 13.132765 gigatons (Island Level).
Although I'm still not sure how we would be able to determine Gear 2nd without Busoshoku or Base Luffy, while at least his Dressrosa Arc Gear 3 would be at least >= Gear 2nd with Busoshoku (since otherwise there'd be next to no need for Gear 3's power boost), and his post-Katakuri Gear 3 would scale to his Gear 4 like it is currently scaled now.
The only possible solution for Gear 2 without Busoshoku is to backscale from Gear 3rd (which as I said should be >= Gear 2 with Busoshoku), and since Gear 2nd currently scales to about 1/4 of Gear 3's AP (due to the Hody Jones scaling), then that would be about 3.283 gigatons for normal Gear 2 (Large Mountain Level+).
However, I don't know how to find Base Luffy's value, since for some reason this wiki doesn't accept the 4.878x multiplier of Gear 2nd provided by Gear 2nd being >= to Base Lucci who had a power level of 4000 while Base Luffy was >= Blueno who had a power level of 820.