Why? Leao is hardly posting better numbers in a much weaker league. Vini is probably the best in the world in that position right now. You haven't come up with a single name yet.
To replace Rashford? You mean like the name I've posted numerous times? Garnacho. You might not agree, but I clearly don't agree with you either. Last season was an anomaly, stop looking in to it so much, look at Rashford's stats over the years... two times, arguably three, he's had what I'd class as a good season, two of those times, have funnily enough come around contract negotiation time, 2019 and last year.
He's hit 30 goals once, in 8 years of being a first team starter. This season I'll be amazed if he even gets to double figures.
Give Garnacho a long run on the left without dropping him for Rashford and I reckon he'll easily out perform Rashford, and already is if you look at assists per 90' and is virtually equal goals per 90'