Dear WOTC,
Give us class options and variant abilities that address classes breaking your own class design guidelines. Furthermore, if you are going to force subclasses under a class (e.g., under the rogue, because the rogue uses light armor and/or is the non-magicial skill specialist) and the introduction of the subclass breaks the design guidelines, provide new variant abilities or options for the core class to prevent breaking the design guidelines.
For those that have not watched the episodes Mearls Happy Fun Hour, Mike Mearls revealed he official class design guidelines and gone into more detail over various episodes. Early on, he also told his audience how they were finalized after several core classes were finished. Here is what I compiled.
1. Players should be playing the character they want to play at first level (Happy Fun Hour: Kraken Sorcerer 1/30/18; 19:24).
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). 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).
4. Taking a subclass should not fundamentally change the character, but further augment the concept. I accidentally deleted the reference for the first time it was said, but I believe it was the 1/30/18 (I will try to verify and update). It, or at least the first half was stated also on 4/4 (about 23:20).
For example, when taking your subclass, you should not be changing your equipment (Happy Fun Hour: Kraken Sorcerer 1/30/18; 19:24). The Valor Bard breaks this and Mike said that the Bard should have had its subclass at first level.
5. Given the above, core classes that receive their subclass at 3rd level should be should be "seeded with enough options at first and second level" to avoid an "awkward transformation" (Happy Fun Hour Kraken Sorcerer).
When coming up with his Vigilante (a.k.a Urban Ranger) subclass, 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.
With the release of the Swashbuckler and Scout Rogue subclasses, Thieve's Cant and even skill and tool proficiencies (e.g. Thieves' Tools) can raise issues with number 2 (irrelevant or forgotten abilities that the player does not want). Not t all Swashbucklers or Scouts are affiliated with the criminal world or thievery. Both subclasses are intended to also cover lightly armored skilled warrior types due to the Rogue's armor, skill selection, expertise, and equipment. While easy to address, and I had posted options on the boards for the Scout (a variant to replace Thieves Cant and another to swapping some proficiencies), it does not excuse the the designers for not addressing the issue officially. New DMs may not feel comfortable making such changes to the rules (I have encountered a few in prior editions ), some groups just want to stick to official rules and options, and, while I am not an AL player, it is my understanding that house rules are not legal in Adventurer's League. Thus, players may be stuck with abilities that go against the player's concept.