It's a great, tough, nuanced question you're asking.
I think ultimately it's not a very bulletproof question for the reasons you stated. "Commit them to disagreeing" should allow us to really explicitly define a disagreement, and (E) really should fall under a "most likely disagree" type umbrella.
Because (E) says "
A central consideration", not "THE central consideration", it allows for the possibility of multiple central considerations.
And you're right. Hector might believe the central considerations are "sufficient artistic merit and sufficient public benefit". If so, he could believe that artistic merit IS a central consideration, but still argue in favor of removing the sculpture based on its failing to achieve sufficient public benefit.
You're gonna have to just live with this as an imperfect question that STILL has a "best" answer, even if the answer is not 100%.
What LSAT thought they had to justify (E) was Hector's move from sentence 1 to sentence 2:
"You may be right about X. However, we should really talk about Y."
They're thinking that switching in such a way indicates that X was not a central consideration.
I think you came up with a cogent loophole around that.
They could have easily fixed (E) and made it bulletproof by changing "a central consideration" to "the central consideration".