It depends on if content was built or is being built around the current system... If you can constantly raise, then it makes the content a lot easier
I think 30 minute cooldowns are premeditated. Look at How Ifrit has a 30 minute window... Coincidence?
Not a chance... 1 rebirth per Ifrit unless you chainspell.... I think that's how they intended it
10 Minute Rebirth + chainspell would make dying on a big boss battle almost unnoticeable... and thats not what the devs want to happen