I don't know, Floyd was a master at using his reach and picking fighters off with his straight right hand. I don't know if Loma could get past his jab and right hand.
If they had similar height and reach it could be very competitive. A 7.5 inch advantage is laughable.
Lomachenko is the fastest and most technical fighter of the moment but he can be hit for a whole bout how demonstrated Campbell last night.
Styles make fights. When the shorter fighter is a bully type with "hands of stone" he stands a better chance against a boxer. When you have a reach disadvantage you need to excel in either speed or power to have a good chance against a longer fighter. At the top level, the skill differences can be miniscule enough that physical differences determine the winner.
Chavez didn't have tremendous speed or power and he had a 66 inch reach. Lomachenko isn't blazing and doesn't hit very hard at all, he has a 65 inch reach. Andre Ward wasn't that fast and was a light hitter, he had a 71 inch in the LHW division.