Full disclosure, I've not progressed in Eureka enough for this to even be relevant to me.

You've got 150 people in an instance, and perhaps not everyone in there is part of the discord but wants to go in. If you want to make sure everyone gets in, and you don't want to risk having your portals "sniped" (it's a public instance and a public dungeon, so really portals are and should be first come, first served) perhaps your group should do the work ahead of time to enable you to claim the portals before they're all available to the public.

If that's too much work for you, then all parties involved should get what they get, and at the end of the day, everyone needs to shop being shitty to each other. People who get into a portal who aren't part of the group shouldn't be harassed or treated poorly because they beat someone to a portal, and if you see someone waiting on a portal, you should probably go look for another one.