This is purely based on assumptions and wishful thinking on your part with no technical analysis whatsoever. Garcia cannot beat one of the 4 best lightweights in the world because he has the same level of defense and footwork as somebody with 1 year of boxing experience.
1. All it took for Campbell to land a cross flush on his jaw was a level-changing feint. You're not supposed to get hit 100% with a cross that wasn't set up by any punches when you're still fresh. You're supposed to instinctively use your arms, upper-body movement or head movement to either make it miss or land at less than 100%. Garcia is incapable of doing so because his only defensive strategy is to step back with his feet, which is the slowest form of defense. As a result, he cannot defend a punch he didn't see coming from a mile away and has to utilize his offense to deter his opponents from attacking him in the first place. When your only mean of effective defense is offense, it screams disaster.
2. Prior to the knockdown and for pretty much the entire fight, Garcia was keeping his lead foot on the inside of Campbell's lead foot and only stepped outside to put together combinations. It's like he doesn't understand you have to move your feet in the ring and it has to be in a non-random way and sometimes, you have to do it preemtively. Yes, he's fast. Yes, he can punch. Yes, he can even throw multiple punches in a row but boxing is 1/3 footwork, 1/3 punches and 1/3 defense against punches. Most importantly, boxing is not a sport where you can defeat fighters of the caliber of Lopez, Loma, Tank or Haney when 2/3 of your game is barely Junior Golden Gloves level, even if you're athletic.