Of course alcohol is a powerful solvent at any concentration, but there are definitely studies[1] that demonstrate 70% being a bit more effective at disinfecting.
That's always been the rule of thumb that I learned growing up too. My dad kept 90% or stronger concentrations for cleaning electrical contacts and other industrial uses, and 70% for first aid and sanitizing, because that's what each was made for.
[1]: https://www.webmd.com/first-aid/ss/rubbing-alcohol-uses