Credibility in any business that offers a service to it's customer is important.
Has Zenimax lost some of it? for me yes, a measurable amount.
Explanation....

I like others are still in the mind set that this is still E.S.O. (Elder Scrolls On-Line), it is not... It is Now E.S.O. Tamriel Unlimited.
There is a actually a big difference there. With the new E.U.L.A. (End User Licence Agreement), that we all had to accept with the 1.6 patch, E.S.O. was no more.
We accepted the "New" version and all it would bring. That there, is a marketing loop hole. Companies can change a lot of terms when they make users "sign" these. It is also a king of a "Grey Area" for me, regarding being sneaky. But, like others have rightfully said, " This is a company, trying to make a profit".
They are not focused on selling the game subscription anymore,(No subscription fees). But have turned towards what? Crown store items?
There is still a sub fee that can be paid by anyone who wants to. I can't see a majority of the newly acquired population going that route though, since many of them came to play only after it has become B2P. So that fee is for the most part going to be held on to by the people that paid for the original subscription. Yes, there maybe some additions of new players in the future.
Can they improve on their credibility? Sure why not. If they feel they want/ need to. That is up to the "bean counters" that run the show.
The first thing they would need to do would be to either change how this game is being advertised or fix some of the issues that have been around from day ONE.
Just as an example. The Lag in Cryrodiil. Because it has spread into the PvE area now.
They have done, an average, to great job in finding and fixing many bugs in the game. And the animations have improved a huge amount; So all is not lost.

One last point. Any company can make and try to sell a product, but if the product is not what it is made out to be, people Will stop using/buying said product. And with MMOs....people do not keep quiet about what they like and do not like. , and their credit cards speak louder than any forum post ever could.

Sorry for the long post, but I tried to explain my point of view fully.