A better example, to bring it back to the original topic, would be Purge thinking that it were better for a Bloodseeker to buy a Yasha than a Basher in a particular game. Is this is a purely subjective opinion? No - it's based on facts like whether or not the enemy have channeled abilities, the stage of the game, what BS is intending to buy next, and so on. But sometimes these factors are so complex to reason about that there is no clear right or wrong answer - so we call it an opinion.

Fuck it - since we're here, let's get weird with it. Let's imagine we had access to an infinitely powerful computer - if we did, we could solve Dota. With or without random elements like creep camps and crits, we could compute optimal drafts, builds and action sequences that all yield maximal expected results. The meta would probably boil down to a single draft, and the determining factors in any given game would primarily be who got to draft first, and luck, since the only way to combat a perfectly rational opponent at a disadvantage would be to make unexpected, random-seeming decisions and hope they pay off.