Not sure how to tell you this but missing weight, and by several pounds, is in fact a huge deal. It's already been explained to you why that is. Not having to cut to make weight is always, I repeat always, an advantage. It's measurable and the commission can actually check a fighter's hydration level. I wrestled so I had to make weight many times. Even though I only cut a little bit of water weight I could feel the toll it took on my body. You clearly don't understand how any of this works.
There are opinions and there are facts, most of what you say are opinions, I have my own as well and those are open for argument anytime you want.
However the facts, which are not open for argument are the following.
Cheating will never be sanctioned in a profesional sport, even if Haney and Garcia decided and agreed upon a "catch favorite substance" illegal fight, or a "choose your favorite brass knuckles" boxing match, nobody would sanction that fight because cheating is not allowed. This is fact, no matter how many millions Garcia pays Haney.
Second fact, being higher or lower in weight has never been illegal or cheating, catch weight fights exists, open weight fights exist in other combat sports, HW boxing exists as well. So then what is the problem? That there are contracts and there are weight classes, if Ryan Garcia signs a contract that he will fight for the belt of a specific weight class and he misses that weight, then it WOULD be cheating if he were still allowed to fight for that belt when he clearly can't make the weight specified for that weight class, therefore the powers that be remove the belt from contention and scrap the original contest. Now what we have two options, cancel the fight or a catch weight fight (or call it what you want) in which Haney accepts 1.5 million dollars to legally fight an opponent that is 3lbs higher. If Haney felt Garcia cheated he could easily sue him for puting his life in danger, but any judge would throw that lawsuit back on his face because he agreed upon the rules of the match and got paid handsomely to do so. Therefore it is NOT cheating. If you accept an arm wrestling match against a guy who paid you in order so he could use both hands vs your one, and you take the money, then lose, you can't say he cheated.
Those are facts. Even with all of that, if you still think Garcia and Haney agreeing to the new rules is cheating, then you simply do not understand how legal contracts work, or the actual meaning of the word cheat. If you tell your wife you are going to sleep with another woman and she says "ok but pay me 1.5 million dollars and we're ok" then ywhen sleep with the other woman, it isn't cheating, it's a contract agreed upon two adults.
Would it be cheating if Garcia still fought for the belt while weighting 143lbs? Absolutely, he is fighting over the weight limit for a belt he can't even make and has a possible advantage over a fighter that actually made the weight, therefore cheating.
But that didn't happen, Garcia didn't fight for the belt, it was an open weight fight for all we care, they decided to go for it.
Last fact. If Garcia used PED's then that's cheating because no one accepted to fight him while on roids, it's that simple.
Now if we go to opinions, those you can argue all you want, I don't care, we all have them.
My opinion in this matter is that Haney and his dad figured Garcia's fatass wouldn't make the weight and they could extract a few mill from the extra lbs while still easily beating him on the next day, as they thought it was going to be an easy night, especially with how much Haney rehydrates, they saw no danger on taking the fight anyway. Something they likely regretted in the very first round.
I have never wrestled in my life, I did box when I was younger and weight is a big deal but it has never been a bigger deal than skill, the guy that used to kick my ass was much smaller than me, because he was much better. If you look at statistics over the years (feel free to google) in boxing, MMA, kickboxing, etc. Adding the amount of times a fighter has been over the limit then compare the times they have won/lost cross checking to the times they were favorite or underdogs, you'd be surprised you end up with a very even average of wins and losses.
In summary, is it an advantage? Sure, it depends on the reason why the weight wasn't made, but it can definitely be an advantage and in some cases a disadvantage.
Was it an advantage in the Garcia fight? I am not sure, a lot of things that happened in that fight did not necesairly have to do with Garcia being bigger but It definitely could be, I never said it wasn't.
Was it cheating? NO.