The Dreamcast era had a large variety, it did not have a high appeal. If it did, the games would not have continued to be failures after SEGA moved away from their own home console business. On the other hand, SEGA Saturn era titles such as Panzer Dragoon, The House of the Dead and Virtua Fighter were all successes, the only Dreamcast era titles being a success was Crazy Taxi.
As for iconic? Space Harrier, Afterburner, Outrun and Super Hang-On are more iconic representations of SEGA than say Rez or Space Channel 5. Both the Streets of Rage series and Eternal Champions would be more readily recognized by non-SEGA fans now than Skies of Arcadia or Jet Set Radio, does that mean we should throw the latter two games out of the window? Of course not (And I would imagine Streets of Rage is also more financially successful than either Skies of Arcadia or JSR combined)
If anything, the Mega Drive era should get the most, this is the true iconic era of SEGA. We ranged from speedy platformers like Sonic the Hedgehog, tactical RPGs like Shining Force, action adventure games like Beyond Oasis or Soleil with a large and beautiful world to over the top action games like Alien Soldier or Ranger X with some brilliant products from their Western branches such as Ecco, Vectorman, Eternal Champions or Comix Zone, something that will alas not possibly be represented. I could go on and on about what the Mega Drive had to offer, the only thing the Dreamcast has an excess of was artsy games.
As for your closing statement, the Mega Drive has the best design and the highest appeal to most but I would not go around claiming it should be over-represented. Nor would I claim AM2 who have not one, not two, not three but several massive games. More so than Sonic Team, one could argue it was thanks to AM2 and Suzuki's brilliance that SEGA is still alive today, when their collapsing console business was eking them closer and closer to bankruptcy, it was the domination of the arcade business that kept them alive but again I would never want AM2 to be the sole developer represented.