Laezel and Shadowheart definitely seem more like rookies. Laezel was raised in a creche but has not been to the Astral Plane (she will tell this to Gale as you explore the world). The Githyanki have to take part in a successful illithid hunt before they can venture to Tunarath. I think she is also terribly unreliable, not because she is a liar, but because the Githyanki are all indoctrinated in the Cult of Personality that is Vlaakith. Shadowheart is mysterious, but strikes me as someone that is not terribly experienced in the world.
Gale has had his power stripped from him (maybe from the tadpole, maybe because of losing the favor of the goddess of magic or absorbing the pocket of the astral into himself).
Wyll may or may not be lying - I can't tell, he will talk about what he was capable of before the mind flayers took him. But he could be lying/exaggerating. I tend to think that it's a combination of both.
Astarion is a vampire spawn. Spawn are slaves to true vampires and have little free will - they are also depicted as fairly uniform in ability. A farmer or a child turned into a vampire spawn is just as dangerous as a wizard or an experienced knight or something. They lose their identity and become vampiric slaves. Astarion is free for the first time in two centuries - I think him being a rogue is a representation of his talents derived from being a spawn. If he was a typical vampire spawn he would be; 1) destroyed immediately by all the sunlight; 2) capable of regeneration; and 3) much, much more powerful than he is. I single Vampire Spawn would tear through a level 1 adventuring party, so it is again clear that the tadpole has changed him substantially.
