Sona is kind of a stupid champ
shes tied for lowest mobility on supports and she has to go into auto attack range to fully deal her passive poke boost and if she is caught by anything she dies faster than you can blink at the rate of 1 teemo per second , all of these things combined = mass feeding
you might as well just afk in base if the enemy support is a thresh or a blitzcrank or a leona or morgana or even taric
or if the mid is an incredibly mobile assasssin or if your jungle is an incredibly mobile tanksassin these 3 things combined will = 99% of your games so you might as well play someone else
if you want heals you play 
heck even 
or 
if you want shields you play 
if you want move speed buffs again or even 
if you want cc you can play 
if you want Damage you play any Apc bot lane because they will do more than sona , im looking at you 
if you want to make hook plays 
if you want to feed and lose your lane while listening to mad beats you play 
if you want insane utility u play bard
even sonas aoe stun ult is outclassed by morganas ult
everything u can pick a sona for can be outdone by a diff support
