I see in a comment below that you're a support main, and I checked out your op.gg... Your average KDA on Janna is fairly decent, yet you have a lower win rate with her than with Leona.
You also just won a game with Leona, which, I'd like to point out that in a 38 minute game you didn't buy a sweeper, but instead kept your yellow trinket the whole time? Odd. Sorry, and I have to point this out too, but you only placed 16 wards throughout the entire game :s 0.42 wards / minute.
Anyways, onto the point of Leona...
While armor is very good on her, you built 0 magic resist against a velkoz. Though the build isn't horrible, it's strange.
Leona is one of my favourite supports. She rocks 2v2 bot lane. She rocks level 2 power spike. She can take out wards w/o sweeper (though apparently you don't buy that anyways).
I've easily turned around so many 2v2 fights where my ADC was about to die and I chain stunned the enemy ADC for so long that we win it and get 2 kills (earlier today for example). She's great at engaging, either R E Q or E Q R. Maxing her W first gives her HUGE bonus defensive stats allowing her to take a lot of damage in team fights, AND she actually does more DPS than a lot of other tank supports (trundle doesn't count, while he's used as support currently, he's not a traditional support).
Also, even though she isn't build for disengage, her disengage is amazing. I was running by myself away from 4 enemies earlier and one well time ult stunned / slowed all of them long enough for me to escape WITHOUT using flash.
I really have an issue with "support mains" complaining about certain champions being too weak when in reality they just don't know how to play them properly. Practice with her, learn new things, use better builds, and I bet you'll find out she's actually a great support.
Good luck! ;)
Edit: Sorry I keep noticing more things, you had more gold that game than the entire enemy team except velkoz. You complained about support champs not having enough gold income, that's what
are for. With Leona, take Relic shield and last hit those minions. In a 38 minute game played properly, you should be near full build. A lot of the time in close games that aren't heavily favoured to one team, I reach full build before most of my teammates as support.
Learn instead of complaning. :)