I agree with you, and one more reason to do so is that with (a)"all + noun = we can use All with a plural noun to make a generalization about an entire group of something."
and then this ALL (b) "refers to the total number of people or things of a group. They are considered as a group and not individually. There are minimum three things in the group.
" Although, for effect of the rule, I would say that with two things it also works, taking (a) on account.http://www.grammar.cl/english/all-every-each.htm
To many it would be tricky because there´s a rule that goes "when we are saying that as totality of items in consideration". Okay, but in the sentence "All the options seem so good to me.
" we are talking as if we are going to evaluate "one by one" to give the answer, not the totality. So, we can´t think the group as one whole to give the answer, the answer comes after considering all and every answer first.
The totality thing is very usual (and works well) with abstract notions, as in:
"Don't cry! All that matters is that you are safe.
Thus, in such case one would use the verb matters
in the singular form.http://www.bbc.co.uk/worldservice/learn ... v266.shtml