I said in a previous post (which was the one the person I replied to quoted) that I realize this already happens without the level boost. I just personally hold the opinion it will make it worse. There will be even more people not even knowing the basics because they level boosted and immediately got tons of abilities all at once and won't have any idea what any of them do.
Everyone learns at different speeds but I think its a well known education fact that most humans learn better with more evenly paced system; learning aspects a few at a time instead throwing them into 40 different new math formulas all at once; it causes information overload which usually leads to more prolonged confusion. They also might get help from fellow players along the way of their leveling journey which helps them learn even more, boosting will skip this too since you won't have to run any group content to level up.
Imagine getting into Titan HM with fresh boosted 50 (or 60) healers or tanks. Players that have been playing for years still can't do this fight without dying or falling off (with the experiences I've seen). I can't imagine being able to clear with healers or tanks who basically just started playing that day and already attempting content that was considered one of the hardest fights in the game (until Titan EX came along) when it was released.
A new player bonus in the content is one thing. A boosted player who doesn't know any of the icons for their abilities since they didn't have to level it from scratch is just going to be bad. You wouldn't even have memorized what spells/abilities are linked to what icon graphic. I can just imagine a healer spamming Esuna thinking that's the icon for Cure when it isn't because they didn't have the leveling process to memorize their icons.
So I still think it will make this problem more prominent.
Judah_Brandt explained the reasons why saying "there already unskilled players so it doesn't matter" is not the right way to go about this quite well so there isn't much need to explain my point of view beyond this.