A fight that feels like it maybe ought to have taken place during the seven year period they overlapped swimming in the same waters at super welter (or light middleweight, if you prefer), from 2010 until 2017, but AFAIK was at no point ever in serious talks. Common opponents include: Yuri "The Boxing Rabbi" Foreman - lost to Cotto via TKO9 in 2010, and to Lara via KO4 in 2017. Delvin Antonio "The Jaguar/D-Rod" Rodriguez - lost to Cotto via TKO3 in 2013, and to Lara via UD12 in 2015. Santos Saúl "Canelo" Álvarez Barragán - defeated Lara via SD in 2014, and Cotto via UD12 in 2015. Austin Dwayne "No Doubt" Trout - defeated Cotto via UD12 in 2012, and lost to Lara via UD12 in 2013. Obviously the Puerto Rican fighter is staring down the barrel of many a disadvantage here, both tale of tape related and stylistically. He is giving up a great deal of height and length (two and eight inches respectively) and there is the glaring fact that Lara is a southpaw - discarding his dominant victory over an injury-nagged Maravilla, previously Cotto had been hit with nearly 50% of power shots on average by the lefty triad of Judah, Pacquiao, and Trout. Walking down and scoring on the Cuban with his slippery movement and rangy pot shots furthermore proved difficult enough for, say, Canelo, who is both taller and has more reach than Cotto. Topping all that off, Lara is a natural and career-long 154lber and not in fact terribly outsized against middleweights - and Cotto's frame was perhaps best suited to welter (a tad short for the division but 140lb altogether ceased to be an option for him just five years after turning pro as he unambiguously outgrew it). Having said all that, most fans & historians probably agree that Miguel is the greater overall fighter than Erislandy - certainly in a p4p sense, if maybe not h2h at 154. Class tells, as they say, and greatness can often trump an otherwise stacked deck. There is also the fact that Cotto is, among his generation, a body puncher nonpareil, with his left hook in particular a game-changer when it could reach you - and various competitors did find degrees of success hitting Lara downstairs (Canelo, Martirosyan, O'Sullivan, and Hurd to different extents). Is there a path then, for Junito to provide a rude awakening for the American Dream, anytime post-Pac?
Cotto had clearly the greater career and was probably genuinely a little better at their respective primes, from a p4p perspective. However, imo, this would have been more than offset by size and the style match up advantages in Lara's favour. Cotto was a big LWW/smallish WW in his prime. Regardless of what or wasn't in his gloves, Margarito was notably bigger and stronger at WW vs Cotto, in a way he wasn't vs Mosley (even allowing for Mosley's greater power). At 5ft 7ins, even down at WW, Cotto has a small frame by modern, day before weigh in, standards. Lara's reach advantage is massive, as you allude to. He was naturally a weight division to a weight division and a half bigger, imo. I appreciate triangle theories aren't always definitive, but that doesn't mean they are never a reasonable indicator. Their respective performances against Trout don't bode well for Miguel in that regard. Furthermore, the things Trout did well that Cotto couldn't overcome - i.e. he got outboxed at range by a pure boxer, with a big reach advantage, who was too big for him to walk down and bully physically - Lara does better.
Cotto was never interested in this fight. He cleverly wouldn't even mention Lara's name from what I remember. Lara could be a bit lazy and judges didn't like his style much, He also had tendency of giving away body shots - so Cotto could have some opportunities here to try to steal rounds and a fight - but focused Lara would have all the tools to win it comfortably.