Where are the checkpoints in temples????????????

Speaks for itself.

Another case that shows none of the devs at GGG have actually taken the time to even attempt building any temple at all.

They would have hotfixed in more checkpoints the moment they started playing and trying to build a temple that isnt just bum-rushing atziri.

Why are portals even allowed to be opened if you have to walk all the way back?

Makes no sense, either have the balls to say, ye no portals you have to run-back, or allow the portal to show up so you can resume where you are without having to walk all the way back, or buy a temporalis.