SAO and MMY have the same problem : They take themselves too seriously and then act dumb.
MMY is good but sometimes it become very silly, which irritates me because it started as the "Anime that would destroy all the anime tropes" but without being a parody.
That's interesting ... because i totally agree with you on SAO being too serious and ending dumb but i don't see why/how you compare it to MMY. MMY does contain "serious" stuff, i mean geopolitical stuff, and MMY is not going dumb as far as i've watched (i did not yet see ep11), i mean it's not about "papa! mama!" and crying all day long.
Btw what does "tropes" mean 
Tropes are story-telling common places, things that generally happen, for example when Yusha meet Maou the common trope would be for him to face the big bad Demon King and save the world. But MMY subvert the trope by having Maou being a hot girl and asking Yusha for saving the world in a non-fairy tell way through geopolitics and economics.
There are so many things in story telling that are common no matter the media or genre, they are generally called trope, try having a look at the SOA page on TV tropes, to have more example of tropes, they have a database of a lot of shows :
http://tvtropes.org/pmwiki/pmwiki.php/LightNovel/SwordArtOnline 
As Maou Yusha sometimes being dumb, here are a few things that I bother me :
- Maou BOOBS : yes it was funny in the first episodes to see Yusha blush with those massive mamba jambas being shoved in his face, but it becomes boring after that. It would have been so much funny if it was just a trick of Maou to get Yusha attention,
Humans like boobs so me make big boobs, and that she could "deflate" chest size later when she got his trust.
- The Harem : There is no reason for the Harem, there is no reason for Maou and Yusha to have a "love story", would have been much better if it was just about business and the love would grow bigger with them. But instead we got the most tiring Anime trope ever with a massive Harem. The only redeeming factor is that Dragon Princess was tired of not receiving attention and she is now made the Young Merchant her new Hero.
- The Plot: I love the geopolitics, economics and scheming, but many times the resolution is completly silly for example when the Humans were holding Gate City instead of Yusha going Beowulf on their asses with got flurry fairies and 10 000 veteran crusaders of a war against demons running away from a headless knight that killed NOBODY, this is impossible. MMY tries to be very serious, but this was a very cheesy way of going about it, isn't Yusha ever going to spill a single drop of blood to create the better world Maou talks about ?
There are some other smaller things, but these are my 3 biggest problems with the show, I like it but it is not one my favorites.
