Binder can call his people when on the island. That does not mean he came there via the never ever. Binder had a wetsuit, he probably used jet skis or something like that.
Binder is a summoner, it requires him to physically get to the place and lay a circle. There is a bloody huge summoning circle on Demonreach which Harry could use to bring bad guys to the island.
This does make me think this would be limited to those in the Never Never, a threat in the mortal world like the Titan couldn’t be summoned in this fashion which would explain the need to get her to the lakeside. She had been hiding out in the mortal world.Remember Bob hid in the mortal world to avoid Mab, if he was in the Never Never could he just have been summoned?
This would suggest summoning creates a temporary congruency between the mortal world and the part of the Never Never where the target is causing an overlap within the circle. Breaking the circle releases them into the mortal world. If done successfully with enough will the target has no choice. If the target is in the mortal world (like Toot) they have a choice, but in Toots case greed overcame his caution.
The Majority of the inmates were likely summoned from the NeverNever to the summoning circle at Demonreach and bound by the Warden and Alfred. This explains why the bad guys don’t know about Demonreach. Harry of course did it the hard way, using Bob on the lake shore. If so it would be unusual for Harry to have a summoning Crystal off the island, it’s use is very limited. Of his opponents only really Puck and Shagnasty really qualify, Cowl if he had succeeded in the Darkhallow and Harry would have to lure them to the lakeshore.
Harry should really try to use the summoning circle to take down Puck, he knows enough about him to summon the Wildfae, and it would be a good test, as well as removing a threat to the future of Chicago.(Puck is from the comics which are cannon, I think Harry beat him with sleight of hand learnt from his dad rather than pure chance, Puck was looking for a Wizard to cheat with magic).
Creating a portal is just punching through to the NeverNever and the congruency isn’t created, it already exists, but may not be the one you desire that is why you need to use the ways to get from point A to point B.