I was simply disagreeing with the statement "We were all bad DMs at one point (when we started)". An inexperienced DM isn't inherently bad, they're just inexperienced. I've played in games with brand new DMs where we all had a lot of fun. Of course they could have done better, every DM could always do better.
You seem to have a different definition of bad DM than I do.
For my part, there are three categories relevant here (that is, DMs I would not call "good DMs"):
1. Harmful DMs. These are people that are actively doing things I consider to be outright bad to and/or for their players, such as the aforementioned active un-personing of a player's character if they don't play the "correct" races, which mostly meant the core four plus a couple old familiar ones like gnomes. And, unfortunately, a significant chunk of advice for DMs in early D&D books really does advocate for stuff like this.
2. Inexperienced/Inept DMs. These are people who mean well, but through inexperience or having developed wrongheaded beliefs or some other thing, they make poor choices with significant negative consequences when sincerely trying to make good ones. The line between this category and the previous can be fuzzy, as the preceding group may feel what they are doing is actually good when it isn't, but in general this group is still possible to reach with
some criticisms, while the preceding group is not.
3. Mediocre DMs. This is where I think a majority of DMs fall. Unfortunately, being a mediocre DM often means folks still make a lot of poor, harmful choices. They just aren't as committed, and the balance of their choices is middling rather than distinctly bad like the previous two.
Well-constructed rules and procedures are extremely helpful for #3 and
usually helpful with #2. Even with #1, though, well-constructed rules and procedures still provide some benefit. Firstly, most outright harmful DMs still feel a need to cement their legitimacy, and thus will work to undermine effective, well-constructed rules that would get in their way in advance. This can act as an extremely effective early warning sign. Secondly, most if not all outright harmful DMs will take steps to insert greater ambiguity, confusion, deception, or deniability, especially if they can do so while avoiding accountability for the insertion. Well-constructed rules make this significantly harder by promoting clarity, transparency, and accountability.
More or less, well-made rules make for an environment that outright harmful DMs will constantly chafe against, and thus provide a subtle but powerful pressure against their participation, while supporting player ability to see, ID, and call out harmful DM behaviors. Poor rules, on the other hand, create a climate where harmful DMs thrive, and where players can be powerless to do anything about it
except "voting with their feet" (which is a significantly bigger ask than many, many proponents claim it is, as they ignore the
social cost of doing so.)
Inexperienced or inept DMs and mediocre are helped immensely by well-made rules, and hampered by poor ones. In some cases, poor rules may even help grow the pool of harmful DMs.