My apologies if you read that as an admonishment. The point was only that it can't be confirmed and is therefore only an opinion, which there is nothing inherently wrong with.
And you're right, the demarcation between top 7 and the middle group of QBs in the league is indeed an opinion, based on how one prefers to measure the performance of quarterbacks. However, regardless of how anyone prefers to measure it, there will be some demarcation between the best group and the next-best group, and if how one views Tannehill doesn't advance him above that demarcation, he isn't meaningfully different from Smith in that regard.
"Top 10" seems to be used here a great deal, when I have yet to see any elaboration of why "top 10" has any inherent meaning. Is it just a nice round number, or does it mean something in terms of distinguishing those 10 QBs from the next-best group?
None of the demarcations have any meaning. Why top 7? Why top 10? IMO top is used because it is a nice round number. Usually the initial group is not a predetermined size. It is the group considered elite. That is usually the top QBs that consistently put up good numbers. Matt Ryan can enter that category with another season or two like last season.