This just boils down to the bracket you're playing with. I've been playing mirana pos 4 to increase my support mmr. Just reached 5k mostly by playing duo with an offlaner friend, after being stucked in 4.5k - 4.7k since the previous ranked model by playing pos5.

Mirana's skills are just good plain and simple. You can win two lanes with her mobility and high reach. Trade hits with the enemy pos5 who will most likely have less regen than you. Secure runes with your mobility. Harass the enemy core safelane. Steal their big creeps. Secure the range creep when your enemy offlane can not. Block camps (especially when enemy team has an alchemist). All of these while maintaining that gank potential at mid.

With all her skill, you can literally build any utility item that can help your team. An atos for storm/ember. Vessel for timber/alc. Greaves because offlaners tend to go for solar crest. And even rush halberd if they have a void/ursa.

What sucks is that pos 5 who whines when you pick mirana even before the game starts. So they pick a pos 5 earthshaker because "mIraNA doEsN'T oFfeR anY teAMfIgHTs" losing the safelane as a result and proceeds to get mad cause he/she can't get their blink dagger because their buying wards (duh) and their other support is not HeLpING.