(The following is from a post I made last year in another thread. The examples I included below are the Valor Bard and the Ranger were two classes mentioned. The Valor Bard clearly violated the design goals while the Ranger issue came up while he was designing a new subclass for his Happy Hour. I would have to go back and see if other specific classes were specifically noted (edit: It appears the videos have been removed from YouTube)).
In various episodes of Mike Mearls's Happy Fun Hour, he revealed WOTC's class guidelines including the level of subclass acquisition. Below I have listed key episodes (for those that want to watch the episodes) and summarized key points. Also, in the Kraken Sorcerer episode, he reveals that some classes break these guidelines, because they were completed before the guidelines were finalized.
Specific points on class on and subclass design from the episodes:
1. Players should be playing the character they want to play at first level (Happy Fun Hour: Kraken Sorcerer 1/30/18; 19:58). "We don't want you want you to feel like you have to wait to play the character that you want to play. We want you to feel you are playing the character as early as possible,preferably, 1st level. Then, as you gain levels, you gain more fun stuff to add to that character You are already playing what you want to play and then you just get more toys to play with as your character gets more abilities" (Happy Fun Hour 4/4/18 24:02-24:25).
2. Core class abilities should be something that all character of the class would want. The core class should allow you to portray the character you want "without gaining abilities that you stop using, feel are irrelevant, or go against what your character is" (Happy Fun Hour: Fighter Warlord 3/16/18 11:50).
3. A core class with a subclass at 3rd level means that "the core class identity is much more distinct, much stronger, and impactful on the character" ("Acrobat Rogue". Happy Fun Hour 2/6/18) which was also stated in Happy Fun Hour: Kraken Sorcerer 1/30/18 (18:58). For example, all rogues pretty much use the same armor, similar weapons. They look the same and are good with skills, but the subclass is how they specialize ("Acrobat Rogue". Happy Fun Hour 2/6/18).
In contrast, a core class with a subclass at first level is "defined by the subclass and is driven by it"- a god of time and a god of war are very distinct and do very different things ("Acrobat Rogue". Happy Fun Hour 2/6/18). Having your class grant a subclass at first level means this how you want to present your self from the start (Happy Fun Hour: Kraken Sorcerer 1/30/18; 18:48)
4. Taking a subclass should not "fundamentally change your character in a seemingly non-sensical way when you gain your subclass" (Happy Fun Hour 4/4 about 23:20), but further augment the concept. For example, when taking your subclass, you should not be changing your equipment (Happy Fun Hour: Kraken Sorcerer 1/30/18; 19:22). The Valor Bard breaks this and Mike said that the Bard should have had its subclass at first level (Happy Fun Hour: Kraken Sorcerer 1/30/18; 22:10).
5. Given the above, core classes that receive their subclass at 3rd level should be "seeded with enough options at first and second level" to avoid an "awkward transformation" (Happy Fun Hour Kraken Sorcerer 1/30/18 21:16).
When coming up with his Vigilante (a.k.a Urban Ranger) subclass (Happy Hour 9/11/18), Mike ran into the problem that the Ranger class itself had no features or options supporting an urban environment. This meant that a player wanting the subclass would be stuck with wilderness abilities that did not fit the concept before finally acquiring the subclass. This meant that the player did not get to play the character concept from the beginning and would then be stuck with unwanted features. Therefore, it broke 1 and 2 in my accumulated list. It would would lead to an "awkward transformation". To rectify the issue, he created new options and a variant feature.
Happy Fun Hour Episodes Referenced
1/30/18 Kraken Sorcerer
2/16/18 Rogue Acrobat
3/16/18 Fighter Warlord
4/4/18 Thief Acrobat (at the start) and Barbarian Maurader see approx 24:02
9/11/18 Ranger Vigilante (Urban Ranger)
