If he wants to grow to be equal to Lydia or us at any point there is no amount of training we can offer him. He's already willing to go on a vision quest to the never-never it was something he was actively contemplating despite the consequences coming from the very mouth of someone who he was very intently listening to.We haven't been 'puting it off' we've been waiting so he can build his skill and power with the training he's been getting. The responsible thing to do before bringing him into possible combat scenarios.
We don't know if it's going to involve combat or not and since literally every time we've left Chicago that's what happened I don't have my hopes up. The notion that your squad can only move as fast as your weakest link is very much true. I wouldn't be against bringing him along low stakes missions (not Vegas not the Hell nuking I wouldn't want Olivia there either with her low long lasting will build) when he has more than a handful of months training as long as he doesn't ruin his relationship with his mother over it.
I am not suggesting that. See above.
I expect his perspective on power and his original intent to run off to fairy land to shift and mature somewhat as he trains under the tutelage of a very experienced magic man surrounded by magictech culture. Knowing intellectually how bad that could've went and actually seeing more of the supernatural first hand with everything that implies are two different things.
I'm not even going to try to address the rest of your post. Your stawmaning the fuck out of me to make a point and I can't say I care for it. That sort of thing heavily discourages interaction from me.
Why would training in our hell affect that outcome when the girl that he's thinking about being equal to and his sister that he's thinking about being equal to or getting in more and more Danger why would not having Supernatural Powers be considered a good thing in any sense.
I say put off because no amount of training actually gets him closer to that goal. The instant he realizes no amount of training will actually close that Gap is the second he talks to Lydia and she helps him facilitate that journey and then he goes.
It is the nature of people to rebel against things they feel a restraining you cannot come because you lack power and the training I'm giving you will not give you that power. This thing that you can do though it may endanger your life though the reward may taste like Ash upon your tongue this journey can change that fact.
There is no Insight on power that can be gained when you have none. It's like trying to gain Insight on dark matter without a sensory array or trying to explain color to a blind person this training may help him survive most average encounters but it has gotten him no closer to his goal and it has made him no more powerful than any other person could be. A magic sword if he ever realizes it is never going to change that.
Nothing in my mind screams weakness more than you cannot come with us while we perform an errand.