Leona mains I need your help!

What's so good about your champ? Why play Leona over any other support? Any tips and tricks for playing her?

So right now I'm in the support playing mood and I decide to play Leona because I haven't in a while. I really like her hard engage and cc but I went against a morg and felt completely useless that game I think she's one of Leona's counters, I'd also like to know how you get around your counters. I feel like she's completely useless against mostly all supports and (one of my go-to supports) does everything she does better. Leona is so linear she has no defense she can't peel once she goes in, either she gets a kill or a summoner but failure to have your teammate follow up will result in the death of Leona because she can't go away and maybe your carry. That's another problem what if you engage at a perfect time with no follow up? she can create confusion for her carry about when or not to go in. Honestly why should I pick a champ that excels at one with when I can pick another that excels at everything?