I couldn't disagree more about the reasons for the series' success. Certainly B5 hasn't had the notoriety of BSG, but then it never had the corporate backing that show or TNG as another example ever did. Personally, I felt the series accomplished its goals for the most and did so well. Along with that there were certainly shortcomings and missed marks; that can't be denied.
Your opinion is certainly valid and I respect your qualifications, but I see it as being in the minority as to which seasons are the best. At least based upon my encounters at various conventions and computer bulletin boards. To call the series a mediocrity depends much upon subjective material. In the end the series is not so widely know, but that hardly means it is mediocre.