First of all its always popular to rag on the top babyface. No offence meant just an observation even The Rock and Austin had severe detractors. Also there seems to be a flavour of the months heel in the IWC as well from time to time. Anderson then Orton now Miz. And ragging on TNA has been "in" since Russo came back and ROH gets praised to the heavens.
Cena is not as bad a worker as the IWC think he is, but he is not as good as the WWE make us believe he is. Also Cena is not the problem its the entire writing/booking and direction of the WWE. Cena being the figurehead at this time is just the one catching a lot of the flack.
Numbers are definitely down, just look at the ratings, but they where down before Cena arrived as the main event face. Profitability on the other hand is up and that is the E's main goal. This has mainly been done due to greater efficiency, international distribution and new technology. Is their current heading a long term sustainable development? Well they won't go out of bussiness that is for sure but profits will stop growing and will eventually go down or bottom out.
But as long as TNA does not get its head out of its behind or another company pops up they will be no1 for a long long long time. Hell a strong no2 would even force changes but that is not happening either.