Gentle can most definitely keep up with Ruby with his quirk that only requires his command in order to pull up the wall instantly (covered the gap in time for when Midoriya charged at him using OFA, which was faster than himself).
Ruby is notably faster than Deku when using her semblance. You are severely underestimating just how much of a speed boosts she gets with her semblance. There is, objectively speaking, no way Gentle could realistically keep up with Ruby the same way he did with Deku, especially if his goal is not to run away.
The invisible barriers still limit her movement greatly and can pretty much rebound her backwards if she collides into one
No, they really don't do much to limit her movement. The only way her movement could notably be limited is if Gentle puts several air barriers around himself. I already discussed why this is not a feasible option for battle.
Constant use of this semblance (That she barely uses as intricately in V3) for physical means will also drain her aura much faster while Gentle's defensive strategies are easily able to keep him on the upper hand stamina wise.
This is true, but if she can dominate him early on in battle (and yes, she absolutely can), then that won't matter much.
Just colliding into him wont do much either since she would need to pretty much revert back in order to deal any mass damage while close, which is way too risky.
She doesn't need to deal mass damage per hit. Besides, if Gentle were to propel himself to the air and she collides with him such that he hits a wall or loses his balance, then this gives her a temporary upper hand. That is more useful than a head-on charge-and-hit. So, unless you are suggesting Gentle is never going to choose to propel himself to the air, that doesn't do much for your argument.
The fight between them really isn't going to last for hours upon hours.
That's not saying much. It doesn't mean the fight can't or won't last longer. It's hard to know precisely how long, and we were never given a scale for how long his quirk lasts. But it is unlikely that it would last hours upon hours, and there is just no evidence whatsoever to suggest that it will last the whole fight, that's ridiculous. Is it a possibility? Yes, it certainly is, but saying it will happen simply because it can is a huge fallacy. If that's the type of argument you want to make, then I don't see how your argument regarding the air barriers holds any weight whatsoever. if Ruby can overcome them, then she will overcome. That's what your logic suggests. And don't get me wrong: I definitely think she realistically would overcome it, but it's not merely because she can, it's because she has more flexibility than you give her credit. I'm only bringing this fallacious version up because if you think the quirk will last the entire fight, then you absolutely have to concede that Ruby will overcome the air barriers. If you don't, then you're simply applying double standards and not being consistent.
