Oblivion had some really weak mechanics design and art direction/lore, not to mention the engine problems and bugs (though some of that was forgivable given the size of the game, not to mention that it's kind of an Elder Scrolls tradition), but I'd argue that saying that ES game have never been made by people with skills is really going too far.
Morrowind did an outstanding job at depicting an alien world and making you feel like a stranger in a strange land and Daggerfall was hugely ambitious, although it fell short of what it set to do.
Also Zenimax/Bethesda has been pushing quite a few new IPs compared to the competition lately. Brink, Hunted and Dishonored are all new IP. Brink, from what I've seen, has been performing well sales-wise despite the really poor critical reception and Hunted: the Demon's Forge was a flop all around. Dishonored looks like it's shaping up well, though who knows whether Arkane will have enough time to iron out the bugs (something that it's a bit of a problem with all of Bethesda's games, it appears). So I'd say that Bethesda actually hiring Obsidian is not as unlikely as you seem to think.