Leo doesn't have the benefit of the MC's "adult" perspective and experience, so he serves as a reminder of the shared bond of being "social misfits" - he's reasonably intelligent, but somewhat self-absorbed, and entirely unsure of himself on the threshold to becoming an adult . . . So yes - rather annoying.
Leo also serves to remind the MC that his original impressions of the people in his life were were very superficial, and he receives unexpected benefits when he allows that knowledge to influence his decisions.
I am at the point that I legit hate best friends or friends when it comes to VNs.
Most of the time they are annoying, like LEO.
Not saying he is the worst, from far it tho.
Honestly unless they are strictly used for the MC to get close to their loved ones
IF YOU KNOW WHAT I MEAN then to me, they serve no purpose in my eyes due to how badly most are written when it comes to VNs that left a lot of bad taste in my mouth
Honestly, I have yet to see a best friend when it comes to VNs that was a legit pal to the MC and not a pest.
Well, maybe in a leap of faith.
I also understand most are used for comedic elements, But I can do without them to be fair.
It makes the experience, for me personally, annoying to deal with when you got someone like Leo in my ear.
But I do see the purpose in some way in general when it comes to this VN and hoping the MC also influence Leo in a better way like he is doing the others and his LIFE experience can also benefit Leo in some way, so he can do a little GROWING UP.
But aye, overall this probably just a ME problem overall which is fine, But I just hate friends or bestfriends in VNs for these reasons alone.