Time gate? I'm not so certain about that. I believe the cap actually incentivizes players to run content. If you miss the cap, you lose those tomes, and there's no way to get them back. What this does to casual players like me is gets me to momentarily abandon my current pursuits to hop into roulettes because losing out on the games current currency just doesn't sit well with me. I'd imagine a lot of other casuals feel the exact same way. If there was no cap, I would not run the same amount of PvE content.

Very similar thing happened when they removed the weekly cap on scrips. I stopped farming them. I quickly noticed how I didn't even need to be doing that. And I was just grinding those scrips for the sake of not losing out on a currency I'm not even using.

Same with current tomes. I use the augmented classical gear for max jobs. I don't run savage or ultimate so I don't need the BiS gear, and mindlessly grinding those tomes is not fun, or a good use of my time online. However, I do acknowledge that doing roulettes does help the community, so I still cap those tomes weekly. It's just a chore.