There actually are plenty of objective metrics comparing them, but more importantly, using subjective insight and opinion isn’t the same as what you’re doing. You’re using blind appeals to authority without actually putting any thought into how those authority figures and that majority came to form those opinions.
I’m all for somebody using subjective insight and opinion to tell me what they think that a defenseman does well, and why their eye test leads them to believe a player is better than the stats indicate. That is something that can absolutely co-exist with thinking critically. Your method of blind appeals to authority and majority isn’t.
To be clear here, I really do appreciate what you’re doing here because you’re being honest about the process that you used to form your opinion. That’s a lot better than the people like the person I initially quoted who use the exact same method as you to form their opinion, but pretend that they formed their opinion based on the eye test. I really do appreciate your honesty.
While there are plenty of objective metrics for the players, they are of little use for comparison as there isn't even an agreement about what a "good" defenseman is. Even then, the metrics don't hold much value as they show the players within separate systems rather than in a vacuum.
We can point to things like points, gf/ga, quality of competition, etc. But doing so doesn't actually tell us much as we don't have an agreement on how important each metric actually is compared to the other metrics. Even then, the player's metrics cannot be separated from the team that the player is on.
As such, it is almost impossible to compare two defensemen against each other in a vacuum.
That is why the appeal to authority is not only convenient but actually a logical move. It saves us time and energy from trying to hash out something to which there isn't actually a satisfying or concrete answer.