The "Marksmen don't scale from levels" meme has been outdated and untrue for years
This idea comes from a time when the exp split in dual lanes was 50/50. However, It has been 60/60 for like 6 years or something. Before this, mid would hit level 6 when bot was level 4 so champions with powerful ults could easily roam and singlehandedly dominate as midgame starts. Now a mid roam is less oppressive.
If you look at levels in game you'll see that solo lanes are normally only 1 level ahead of bot lane and generally the ADC will catch up if they focus on farming. There isn't nearly as much of a difference in levels over the course of the game as people believe.
The biggest thing regarding levels about mid lane is hitting 6 one level sooner than bot, so champions with powerful ults benefit from that. However, some ADCs have a very powerful ult such as Ashe but we don't play her mid. So there is a lot more to it than how good you are upon hitting level 6. And of course, all of the things that make a good mid champ are known, but I'm going to skip over that stuff and talk about bot lane.
What really makes for a good bot lane carry is the ability to consistently farm the lane when there are two lane opponents. Two lane opponents means more harrass or kill pressure and there isn't a support that can negate that to allow for a melee champion to farm reliably. Of course in some matchups yes but you have to basically just outpick the fuck out of them in both your support and your carry. So usually you need a ranged autoattack to consistently get all the farm.
So the idea that melee carries or bruisers would need full exp to go bot lane is misguided. Hitting levels sooner would be a small advantage generally, but it depends on the champs you are playing. If you are playing a kill lane then it would be very helpful, but then you are more likely to be playing champs like Panth, Mages, Assassins, alongside supports like Leona, Blitz, Alistar. Or another way you can take advantage of hitting levels earlier is using a wombo combo of ults. But melee carries or bruisers generally would not get as much benefit in comparison to mages, assassins, and other aggressive early gamers or champs with big ults.
