Immersion and roleplaying are nice for people I guess, but shouldn't matter for mechanics. Otherwise we should have stamina meters and have to rest after swinging 20 times, and all be dead from not eating/drinking. If mechanics ever don't make sense to you, just imagine a wizard did it.
That said, I don't see how you're getting 6 out of 7 seconds uptime.
Everybody gets 4 tumble charges, mobility adds 1 for 5. You get a recharge every 6 seconds.
So... for the first 7 seconds.
Tumble (charge 1) - 95% dodge for 1 second
Tumble (charge 2) - 95% dodge for 1 second
Tumble (charge 3) - 95% dodge for 1 second
Tumble (charge 4) - 95% dodge for 1 second
Tumble (mobility) - 95% dodge for 1 second
1 second without 95% dodge after which 6 seconds have elapsed and you now get a charge back
Tumble (re-charge) - 95% dodge for 1 second
At which point another character could intimidate, get aggro and start the whole process over again.
I am sure players would never take advantage of this.