The opposite of 'objective' is not 'subjective.'
Yes, for marketing execution objectivity can be useful - metrics, year-over-year comps, and ROI help measure costs... but even these are no longer objective once we begin to opine about what the numbers 'mean' for our marketing.
Just because it can be measured doesn't mean that's what is important... or meaningful for us.
Objectivity is a cover for our insecurity - our stubbornness to admit we need to try something else while we appeal to this or that comp claiming it should be working.
We will be measured, and metrics can be terribly useful but only on the downside... measuring failures... comparing our numbers to others' numbers... CAC v. LTV (but remember long term value is a projection... based on past performance - and as anyone knows, past performance is not a guarantee of future performance).
For successes, metrics don't mean what we're doing is the best thing (rising tide lift all boats, after all). Even our success can't be taken as objective.
What many call 'objective' metrics can help the emotionally mature to fail fast - and failing fast is the best measure of future success.
And this means the opposite of 'objective' is not 'subjective' - it's everything in the neighborhood of unapologetic marketing.