The midi range, not the tweeter, is the most important driver in a speaker.

It's more interesting to discuss in term of midrange driver size.  Some people prefer smaller size mid for speed and clarity.  Mine has to be at least 5in large so they can better integrated to the 8in. bass at the low frequencies for example.  

Also I prefer the mid not playing at high frequencies where the tweeter should be playing on its own.  I would say 7KHz is the cutt off where the mid shouldn't interfere with the tweeter playing after this.

Sure if you have a 3in. mid that can play at much higher than 7KHz but then it would compromise the low frequencies.  It's all a trade off.  

To think about it, everything else being equal, the mid probably is more important than the tweeter.  But what's more important is the xover.  The designer will ultimately be the final decider as to the final sound.

As for the mention of the Thor, I do have a bit of a soft spot for the Seas Magnesium drivers. They have a unique warmness on the mid and lower mid but very natural, and at the same time, very detail like a hard cone. It took a bit of time to break in and probably may be the longest of any drivers I’ve had. At first they sound a bit cold and clinical, but once fully broken in, it’s all fine. They have a bit of a break up so just be mindful of the xover.

I currently have a pair of speakers that use the Seas Nextel 5.5in driver and the magnesium has the exact the same dimension so it’s a one to one swap. Hm... I have might an itch to get a pair.

But is the mid more important?  Probably but it needs the right tweeter to make a perfect dance partner.