Think the reason she never really tried to kill Claude and Dimitri again is because the first time failed and she had other priorities after that. The fact the flame emperor put Kostas to the job is proof enough that Edelgard wanted the other two lords dead and right their deaths off as a bandit attack and be done with it. It's certainly not out character for to take big risk and sacrifices for the future of her goals.
No matter how you look it's clear that she wanted those two dead. The plan itself was clearly botched but her intentions are there. How I see it the plan was suppose to work out with the bandits attacking the students and in the chaos she would slip away. Their death would easily be explained as an unfortunate run in with bandits. However Claude who was of the people she wanted really dead and likely made a high priority target manged ran away leading and that ultimate lead to the events in the prologue. It was said that Claude bailed out first while Dimitri though he was acting as a decoy.
It depends I guess a sniper is going to have their work cut out for them with bow knights being a master class. I do think some advance classes will get skills that can keep them up to pair for master classes at least initially or have some niche.
Unlocking a budding talent should turn it a strength marked by a blue up arrow. But as a mage how much use she will get out of isn't certain. If she has low strength grows she may not be able to use the sword skill to the fullest potential but that depends on the skill she learns from it.
When ever their are multiple lords in a game there is always one that takes the spotlight as the main lord. Like Ike in Radiant dawn, Alm in echoes, and so on.
Still it is seems like it would be much more work to recruit magic characters with byelth especially if you want multiple ones. I would have expected them to be more balanced in terms of stats since you can't customize them.
I have a feeling that they are going to make higher difficult DLC or a latter update. If lunatic is in the game I am not sure why they didn't make available from the start.