Planar binding is a summoning spell, the least version of which comes online at level 5 for wizards. I don't know why its irrelevant to discussion of the power of summoning in 3.5.
...And I don't claim to be an expert in "optimal(tm)" 3.5 play, but something can be "strong" and still be "not the best option for the strongest classes in the game."
My claim wasn't that players hated high level play, but that DMs do. It takes me 3-4 times as long to prepare for my 10th level group as it does for my 1st level group, and a lot of this is driven by me having to account for their numerous magic items and abilities. It's a lot harder to tune in the difficulty and manage rewards at that level, as well as manage the flow and information of the campaign.
You have not know true terror until a player just says "yeah, actually I have teleport lets just go to [place you haven't remotely prepared yet] right now."