It seems obvious that you are vastly overestimating the capabilities of the eight gates. They increase his speed and power but neither have been shown to be very impressive in comparison to the top shinobi. Even with seven gates open he needed Bee to throw him to catch up to Kisame, even with a head start Guy should have been able to catch up to him in time but he didn't.It's obvious that you're not up to par with the full capabilities of Might Gai... I would put Gai up against anyone in the series(excluding SO6P of coursre) as the winner. but only with the 8th gate open. And this is if he needs to go all out and die for the cause.
People give Guy too much credit, I mean if his strength was that impressive then he wouldn't have needed to go to the seventh gate just to beat a weak Kisame without Samehada.
The gates don't seem to be as much of a power boost as Sage mode or raiton armor but everyone thinks that it is.Everyone in Konoha knows that Guy uses the gates and taijutsu solely so they know what he is capable of, and they were never asking him to fight the big battles like they were Naruto or Kakashi.
Honestly if you would stack up Guy against pretty much anybody in the Naruto Universe than you are pretty much by definition a fanboy.
Minato, Nagato/Pain, Hiruzen, hashirama, Tobirama, Oro, Jiraiya, Itachi, Sasuke, Naruto, Madara, A, Oonoki, Mizukage, maybe Kakashi, Kabuto, Yamato, Danzo, Kisame with Samehada, Deidara, Sasori, Hidan, Kakuzu, Mu, Bee, maybe Darui, and some other people I can't think of can all beat Guy.
Don't kid around.