I just had a really cool idea for a fic I might incorporate one day.
Basically, Gai's team mates on team Choza were actually two very talented and intelligent kids who were older than him, so sometimes they tried to give him advice. One day Genma and Ebisu were watching Gai train while they took a break (no one can keep up with a hyper 7 year old Gai), and Genma called out something like:
Genma: Hey. Your taijutsu is already good enough. Maybe it's time to incorporate ninjutsu into your fighting style. After all, taijutsu can only take you so far.
Gai: No way! I'm going to prove that with Taijutsu alone, you can be a great ninja!
Genma: Maybe a tolerable ninja...
Ebisu: What he means is Gai, *stopping a fight before it starts* is that Taijutsu alone is a bit old fashioned. It can't compete with ninjutsu long term or genjutsu for that matter. Afterall, you can't punch your way out of an illusion. And what if someone sent something like, I dunno, a big wave of water at you! What are you going to do?
Gai: Hmm....I guess... I'M GOING TO PUNCH THE WATERFALL SO HARD IT GOES BACKWARDS!!!!
Genma: You're hopeless. *goes back to laying down while Gai does another 400 push ups*
And then we have a fast forward sequence, to Gai facing down Kisame who has basically created a tsunami and is sending the entire ocean at Gai, and Gai's plan is naturally, to punch the ocean so hard it will take Kisame with it.
In the end, Gai proved taijutsu was far from outdated.