Berman made mistakes, like any human being. But he kept compounding his own mistakes by making worse ones as time went on. TNG went fine, but he made a few mistakes there. Then with DS9, he made a whole host of them, and the great show that it turned out to be occurred mostly in spite of him. Some of the best facets of DS9, Berman was against. The dominion war story arc, loosing DS9 to them, was opposed by Berman. The episode "In the Pale Moonlight" he felt was anti-Roddenberry, which normally makes it bad, but in this case, the episode was brilliance. He was too short-sighted to see his own errors. In Voyager, they just kept getting worse. His greatest mistake of all was in promoting people like Brannon Braga, who really holds a lot of the blame bag for the final years of Trek's errors.
Spiner's defense of Berman is based totally on what Berman did with TNG and it's films. And if you where Spiner, what Berman did with TNG and it's films was fine and dandy, especially the films which gave so much more amplified focus on Spiner and Stewart and very much ignored the rest of the cast in contradiction to the form and theme of TNG. So of course Spiner thinks Berman did a good job. He, likes those he's critisising for being critical of Berman, doesn't know what he's talking about. All Spiner knows about in any detail is TNG and the TNG films. The problems and errors of Rick Berman as time went on in through DS9, VGR, ENT, and the problems many of us found with the TNG films, all don't exist in Spiner's mind.
Pot, Kettle, Black, Brent. Sorry, bud. You missed the boat on this one.
But, by the same token, this guy produced 25 seasons' worth of episodes for 18 years, hiring and working with some of the best writers in the biz (Michael Piller, Jeri Taylor, Ronald D. Moore, Joe Menosky, Brian Taylor, Ira Steven Behr, Peter Allen Fields, etc.). That's an accomplishment, no matter how you put it.
And he also alienated all of them. Or did you miss how they all quit while Berman stuck around with his worst mistake, Braga, gaining more and more power and influence, eventually leading to the demise of the Trek we knew?
Berman isn't the villain. I'll give him that. Berman is the ignorant short-sighted fool, responsible for loosing all the above listed talent and replacing it with Brannon Braga.