Not fully a correct analogy there. A better one would be to say that DMM and Nutaku are both car sellers and Aigis is the car.
So you'd be blaming DMM for buying a faulty car from Nutaku.

DMM is not developing aigis, it's developed by devs who decided to put it on DMM and later try out putting it on Nutaku. The devs make the decision, not Nutaku or DMM.

In that sense, it is both Nutaku's and the dev's fault.

The start of the game was very slow paced with a new event every month or so and they picked up way too late when many who liked the game just jumped to their japanese version instead and had already given the game a rumour of being crap and how "The DMM version is just so much better". This can be blamed mainly on the devs that were too cowardly to go all out in the start to get more people to play and stay on it asap with their "we will add content faster if we get more players" logic.

However, once they picked up the pace it was also kind of Nutaku's fault for not blowing up with advertising to get more people as well as seemingly knowing the game was in a declining state and somehow refusing to tell the situation to the customers, that the devs decided to pull most of their stops and want to see if they can still make it profitable. Honesty is the best way to get long lasting customers that trust you.

All in all both Nutaku and devs are to blame, but DMM should most likely not be blamed for this part. Whether the "not profitable" part was truly the actual reason or whether it was due to nutaku's reputation or the devs simply earning so much more on the DMM version, we won't know. But we can still blame them both! :P

Whether you can still play on DMM and thus giving the devs more popularity is up to each one of us. Personally i am still playing on DMM. I started there 2 years back and have played there ever since. However it is perfectly understandable if you do not want to play it on DMM either out of principle and reasons mentioned above.