Does Oda Think the Emperors and Admirals Are Comparable?

Comparable yes. Equal no

No

I'd say they're meant to be within a tier of each other, to the point that your standard Admiral would be able to solidly contend with your standard Emperor, but still lose out by a decisive notch in the end.

This. Akainu is probably the only one who might be Yonko tier.

I don't think there's such a thing as emperor level or admiral level to begin with but the strongest emperor (Shanks) is above any admiral so there's that.

Emperor’s mid-diff Admirals. That’s what Oda thinks.