What I'm saying is that he won't trap himself with them. He'll trap them with him and the rest of his party. Going in alone is a stupid move, and you can't balance an item based on the hope that the PCs will be stupid.
If his Defender was capable of pretecting himself outside of the orb, he should be capable of protecting him inside it. If he isn't capable, then the orb is immaterial because the wizard is dead.
Fine, so you have your party of 5 PC's. I assume you want all of them in the sphere? Let's say you have a Fighter, Paladin, Rogue, Wizard and Cleric (easier for my chart below). Let's say it looks like this:
xxxxx
xxxxx
xxxxx
xxFPx
xRWC
That's a pretty good defensive setup with the Defenders in front, and it allows ample space to fit monsters inside. Now, that gargantuan dragon you're fighting? Yeah, he won't fit. So instead, we'll go with something a bit smaller...maybe a large creature? You can fit two of them in the orb with the PC's in the current configuration.
Even if we go with medium sized though, you're only going to get a few in there. If you actually get one of the enemy squishies, like a controller, then you could be in for some hurt because your whole party is now in a tight little bunch. If there's some skirmishers it could also pose a problem because they would probably focus fire with ranged attacks on the Wizard, and the Fighter and Pally will have a hard stopping that completely if the enemy has any Soldiers or Brutes with them.
There's a lot of pitfalls to putting yourself into a 5x5 square, but you're not really seeing them. Unless the DM is asleep at the wheel, he should be able to take advantage of them. If all the PC's are bunched to get in the sphere, then his monsters can do whatever they want while the whole party is in the sphere. If not all the PC's are in the sphere, then not only were the monsters split, but the party too! It's not just an automatic win button like you seem to think.
Each and every one of those abilities leaves the current terrain intact, and only modifies it. If you think teleporting to a pocket dimension of your choosing and web are the same, we may as well stop here because we're on completely different wavelengths.
I didn't say they were the same, just similar. In some ways, Web is actually a more powerful ability. The Wizard doesn't need to be within it's effects, it's ranged, doesn't cost a sustain minor (which means he can use
another power that requires a sustain minor) and it permanently alters the terrain for the duration of the encounter. The orb only "alters" it for the time that the party is in the sphere. Once they drop back into reality, they'll be right back in the middle of your carefully designed terrain, with all the rest of the monsters from the encounter to deal with.
So yeah, I think it's a perfectly valid comparison. The Orb has additional controlling effects that Web does not, but Web permanently alters the terrain in a powerful way and at no cost to the caster.