- Prestige classes eroded the sense of class identity, while simultaneously giving players false hope of abilities they would likely never reach. Players created "builds" to go to level 20, but still never really got beyond level 10. This meant the game started at level 1, but the characters didn't feel complete until level 8.
PrCs were an optional rule. Even if used, each was subject to the DM's approval. Personally, as a DM, I preferred using UA style class variants and variant abilities, DMG variants (e.g. variant spell lists), and a few third party base classes. As a last resort, I used the 0/0 multiclassing rules from the 3.0 DMG.
- It was really obnoxious as a DM to create NPCs or to adjust monsters. Even if you had digital tools, this took much longer than it should.
True. However, I never understood the need many DMs had for worrying about this stuff unless they were publishing their work.
- ECL did not work.
Again, true. However, I also saw many DMs misunderstanding and misusing CR and ECL. Furthermore, the DMG also discussed that not all encounters need to be tailored encounters (i.e. those taking into account character level vs CR and ECL). According to the DMG, it was perfectly fine to include status quo encounters (those in which creatures were placed at a location because it made sense) or even just using status quo encounters.
- Multiclassing was super abusive because of how abilities were gained from new classes.
I didn't have too many issues except for multiclassing granting proficiency in all of a classes's armor and weapon proficiencies, and good saves. Personally, I house ruled this.
- Descending BAB made the math needlessly complicated. I suspect the game would have been much better balanced if BAB was the same for all attacks.
Can you clarify this? What do you mean by descending BAB? As for a unified BAB for all classes, personally, I dislike this in 4e and 5e. What I did dislike is extra attacks being determined by BAB from all classes.