^This.
I switched to 120 after years of playing 130. 120 doesn't feel floppy at all. Keep in mind it's the mass of the string that counts, not the thickness. If the metal used is denser or wound more tightly, a narrower gauge string can have tension equal to or even greater than a thicker string at the same pitch and scale.
I'm very well versed on the Physics involved, and yes, you could in theory make a string where a 120 would have as much tension as a 130. To do that, you'd need to use something with significantly different density. I am unaware of anyone using anything but various iron/steel alloys in string construction, all of which have very similar densities. Alloy 52 is the most different density wise of anything people are using, and you get about 5% density rise from using that - but only on the windings - the core is still regular steel, so you're going to get less than 5% change - cal lit 4%. The change you get form going from 120 to 130, which involves a square (it gets bigger in 2 directions when you increase the diameter) is 17.4 %. The diameter of a string determines its linear mass density, and therefore its tension at a given pitch, more that the specific alloy does. If someone starts making strings with Platinum windings, your point becomes very relevant, but those would lose a lot of level and be ungodly expensive to make, so I'm guessing that won't happen.
