I confess, I'm rubbish at estimating ranges. Sue me. ?
One thing I've noticed though, so is everyone else. Next time you run a sniper/DMR try standing at the back of the line out in the open, you'll see players rattling away at you on full auto and their ammo hitting the ground 20m before it reaches you. Seriously, try it.
This device albeit expensive allows me to do 2 things - get the exact effective range of any gun I use (not only airsoft) and see exactly how far other players are away from me (I lase a nearby tree or whatever not the actual player) meaning I can adjust accordingly and hit them 1st time.
A lot of players think nothing of dropping up to £1000 on a posh RIF, IMO if you're doing that you may as well squeeze every drop of effective range out of it..
You're quite right though, simply practicing will allow more effective range guestimation. Horses for courses. ?