18 year old International prospect who would be a pretty good get but he has a 5 makeup. My thought is he probably won’t come close to reaching his potential with a 5 makeup. It would be different if he were a more fully developed 21 year old but buyer beware for an 18 year old. Is my take applicable or am I being overly pessimistic?

I might be wrong on this but I don't think that is entirely how makeup works. I think development for a prospect has more to do with playing time and coaches. Where the 5 makeup will get you is the player will probably start dropping off stats around when they are 27-28 years old. And if they get injured no amount of medical will help them get their ratings back.

When I'm drafting I take the best player based off of key ratings (Splits, contact, power, fielding, control etc) and don't worry too much about the rest.

I agree with hockey with the caveat that IF there were going to be a MU rating that would hinder development, under 10 would be the guy IMO.

I'd be interested in seeing him develop.

I don't even pay attention to that rating anymore. If there's any impact on any aspect of the game (prospect development, late career decline) I haven't noticed. With the caveat that I don't run a medical budget so I wouldn't notice any impact to injuries regardless.