I didn't get much feeling of respect from the pre-Hudlin books. I mean, how many times did Namor call T'challa a fool or belittle his decisions? In Sturm and Drang, there was almost WWIII, because of what the other monarchs considered T'challa's ... non-practical decisions not to mention hypocrisy. And how Namor got dragged into Deviant Lemuria business ... I don't know. Anyway, there have been too many retcons, so I'm not sure how long he's been king now, but remember, T'challa is the youngest person in that room. IIRC, he had the least leadership experience also. And the solution to that conflict rested completely on Namor cleaning up T'challa's mess by being the bigger man and the monarch who cared more for his people then his personal reputation.
TBH, there just aren't that many (male) surface dwellers that Namor respects. As much as I LOVE their team-ups, depending who writes them, I don't think Namor respects Doom all that much at times. And people that write Namor and Magneto, forgot that there was ZERO resolution / absolution to the monumental crap that Magneto pulled by threatening both Lady Dorma and Susan Richards, as well as dragging Atlantis into yet another conflict with the surface world back in FF 102-104. As well as Namor's fabulous reaction to Magneto here:
Those few pre-Hudlin appearances do show there isn't a huge, longstanding rivalry between Namor and T'challa, because they just do NOT interact. The what, two? interactions were either random or manufactured via a third party, like the Deviant Lemurians, or criminal Atlanteans and Wakandans. They show Namor is NOT interested in a conflict. And they also show they don't much care for each other.
The Hudlin interactions don't count, IMO, because Hudlin wrote just about every hero LOVING T'challa and kowtowing to him. That's just not Namor.