Except the requirements for a good chunk of those spells require you giving augments to characters that are going to leave long before the game actually gives you good ones. Its actually tough in the beginning cause you get a few really good ones but have to sacrifice them to Edward or Yang to get their skills and even then, you may not acquire the extra augments they give until much later.
To be honest, most of the augments are hardly game-breakers. Fast Talker is a great ability but it is hardly an "instant cast" ability. Omnicast has never worked properly for me and duel cast was a spell I had to hold onto cause I acquired long before I got the character I wanted to give it to. Not to mention the amount of augments your characters can actually use is very limited. Basically whatever you have on your attack menu (basically five slots) so you sometimes have to sacrifice good abilites for others.
Its really not that easy with a guide and and considering how nasty the enemies in the last two dungeons get, its all fair, the only ability that seems broken is Limit Break but since you only acquire it after you beat the game and can only use it in a new game + where all your characters are turned back to lv.1 its a moot issue cause you literally have to have end game levels to take advantage of it.
The augment system only becomes a game breaker when you start doing the new game+ since you finally start doubling up some abilites but most people probably won't play the game past the first run.