I would let him move back. With a caveat - you haven’t said much about the aggression. Depending on the nature/extent of this previously and whether there is any sign this has improved that might change my view. None of the other issues you list would be an impediment, in my household, to a child coming back to live at home.
I speak as a mother of a 17 year old with a very serious mental illness. I could not envisage a time when I would refuse her a home with us.
The people who speak of “enabling” in this scenario have got it wrong. If you don’t allow him back he will likely continue as he is (or get worse). You will not be “enabling” his cannabis use or his depression by letting him return. I do not think this is a “cruel to be kind” situation at all.
Given he is in decently paid work and living in a relatively low cost housing set up (shared housing being one of the cheaper options) I hazard that his desire to come home is not motivated by financial considerations.
Work as a chef is stressful and tiring. Drug use is endemic in the hospitality trade. He will struggle to abstain entirely from cannabis. Making that a condition of his returning is pointless. You might as well just say no. I’d make it a condition he does not smoke on your property. And that he engages in therapeutic work. I am not condoning the drug use. Just being realistic.
I believe that this is is a fairly straight trade between your well-being and his. I have almost no doubt from what you say of him that he would be hugely better off living back with you. Depression is crippling and even living in a shared house and with regular work he may be extremely lonely and socially isolated. But I also have no doubt that his return to the family home will cause you stress and will strain your relationship with your husband (however good and patient a stepfather he is, your son is not his son and I do believe this would be an added strain - I also believe it is probably the larger part of why you might be inclined to say no to your son).
If your son were younger I’d say that the choice between his welfare and yours would be clearly weighted in his favour. With your son aged 24 you would not be wrong to decide to put the needs of you and your husband first. But since you have asked the question my answer is that in your position I would let him move back.
Good luck with whatever you decide.
Dealing with the mental illness of our children is hugely stressful.