Any tradeoff deals with "contradictory statements". Doesn't mean we should always side with one side on a tradeoff.
Nobody said anything about "fully secure" and some arbitrarily "fully useful" combined, anyway.
For certain people it could be 100% fully useful with just access to a few fixed folders and a few fixed APIs.
Many of us don't want it to drive our lives, just do some specific this or that.
This year we've learned that If a SOTA LLM decides that the sandbox is standing between it and its current objective: well, it has the ability, the time, and literally nothing better to do all day. Odds are, if you've configured the sandbox for anything useful, you've also provided a crack it can use to get out.
Again, doesn't make a sandbox entirely useless. Does mean you can't just put it in a really tight box and call the job done. If anything, the strict sandbox might even hurt, because it's more likely to get in the way.
(By analogy: consider the safety issues posed by a dam without a spillway.)