Huerta's losses were against Kenny Florian and Gray Maynard, then Pat Curran (future Bellator champion) and Eddie Alvarez, then War Machine during one of War Machine's rare pinnacle performances [War Machine might have a lot of personal issues, but as a fighter, when he was on point, he had so much heart and power that it was really a sight to behold], and a Jiu-Jitsu world champion who was about 5 inches taller than him, had developed a very strong Muay Thai game training with Lumpinee and Rajadamnern champions, and was fighting at welterweight in Zorobabel Moreira. His last two losses have also been very competitive fights, even though he handily lost 'em both, and they were against a former Legend FC champion with an extremely effective basic-boxing game (I've never seen a fighter who's striking arsenal is built entirely around the 1-2-3 combo who's so effective with it) and high-level Judo in Koji Ando, and an athletic Jiu-Jitsu champion who has a very hard-hitting, unorthodox and idiosyncratic striking style in Ariel Sexton.
In all of his losses, though, he was very competitive, and you can't say in one of those fights that he was truly dominated. And they were all against very good fighters. It wasn't like Huerta shit the bed with his performances, he was doing good in 'em, and he's been evolving as a martial artist continually over the years, so the fact that these guys were able to beat him says something good. He's also currently on a two-fight winning streak, his first such streak since 2007, and they've both been wins against very good fighters in another former Legend FC champion in Adrian Pang (who I think was something like 22-9 going into the fight) and a TUF runner-up. He's gone 5-8 since 2008, but he's 3-2 since 2014.
Guillards losses were giant upsets, mainly once you take into account how rabid his fanbase was about how sure they were he was gonna dominate the division, and many of them were very brutal. Joe Luazon knocking him down with a counter-jab (I think it was) and finishing him with a choke less than a minute in, derailing his peak hype horribly; Jim Miller submitting him again, rebounding with that horribly lackadaisical performance against Fabricio Camoes, getting knocked out in a minute by Donald Cerrone and losing a way-more-one-sided-than-the-scorecards-read split-decision against Jamie Varner. Getting dominated by Michael Johnson, losing in more one-sided split decisions against Justin Gaethje and Brandon Girtz, getting KO'd by Derek Campos, moving up to welterweight and then middleweight just cuz' he doesn't wanna dehydrate anymore and still losing...
Guillard's losses are against very good fighters, too, but, even including the David Rickels fight as a win, he's gone 4-12 since he fought Joe Lauzon, and he's currently on a four-fight losing streak and 1-7 over his last 8. Not only that, but his last three victories are guys that are like stylistic gifts for Melvin. Two slow boxers in Mac Danzig and JZ Cavalcante (especially given how JZ at his peak was a grappler and his knees were so shot he couldn't shoot for takedowns anymore, like Ken Shamrock before him), and the once-iron-chinned-but-by-then-glass-chinned David Rickels. And now there are rumors that he barely trains.