1. Most players wouldn't even notice at that level. Especially new players who aren't parsing, and any vet of MMOs knows endgame is where it's at. But I already ceded that a compromise was necessary.
2. I honestly have no idea what "copy-driven progress" is. But you're wrong. Experience is the best way to learn, and having most of your skills at level 15 would do wonders for players leveling up, as they don't have to change their rotation every 5-10 levels.
3. No one is going to be excluding new players from leveling dungeons because they don't do enough DPS. My suggestion was to give EVERYONE all of their class skills immediately, not just players at max level. If you're going to excluded a new player from a leveling dungeon because they don't have the top level understanding of the job, then you would have excluded them anyways. No way to promote toxicity, though I feel this point was due to a misunderstanding of my suggestion.
4. All of the content is mostly invalidated anyways. I can do leveling dungeons in my sleep as is. I did Sunken Temple of Qarn on White Mage last week and the tank pulled all the way to the first boss and we survived. At level. I agree they could be more difficult, but that doesn't mean they can't be fun by letting us have more skills and some semblance of a functional rotation. This is a casual game unless you're in Savage, and the leveling dungeons reflect that. Giving us more skills doesn't change that. They would be scaled anyways.
The early game is already severely skewed by virtue of balance being for endgame. All the jobs feel handicapped at low levels due to their rotations being so vastly different at 70, and this is only going to get worse. The only real exception to this is White Mage and Scholar (maybe Astro, haven't played it) since they have the same DPS skills at level 20 as 70 (save a few), just less powerful. Healing skills is the only fundamental change. It needs to be roughly balanced, but being able to rip through Sastasha in 12-15 minutes instead of 30 doesn't deter new players. If anything, it attracts them, as the early story and leveling will be much faster. This is the sort of balance I mean. Obviously jobs need to be roughly balanced, though it's far less important at 30 than 70. For example, red mages are extremely powerful early on due to having many of their main abilities at low level, yet are one of the weakest DPS at 70. The jobs don't need to reflect themselves at 70 damage-wise. However, I personally know 4 or 5 people that have picked up the trial, and quit because the early game is too slow and boring. And they're right.