I agree with you that 'let and 'with are redundant (although I still disagree about 'fn and 'def).
But I think the difference between the 'let and 'with forms would be removed better simply by removing the implicit progn. This was brought up previously in http://arclanguage.org/item?id=3234 .
This would allow (let a 1 form) like the current 'let, or (let a 1 b 2 form) like the current 'with. For multiple statements you would need (let a 1 (do forms)), but pg already said how he liked that 'do highlighted non-functional code.
