So a leona who has cooldowns all timing out should not try and save the adc by sacrificing themself? Here's another scenario: The adc sucks ass and won't engage with leona ever, which negates her whole reason for being there. You're looking at it as the support's fault when it could have been the adc or even a jungler's poor decisions that led to that kda.
This is all situational. If I was that leona and my adc wasn't at 14 kills then I'd be upset, but overall, that kda can be seen a bunch of ways. If the other two lanes are winning and that support died 7 times to feed 14 kills or mroe to the adc then it's worth it by the time the game is over. Leona still has her stun and her ultimate to make use of AND their adc should be hitting for a ton and shredding the enemy team.
See how if we look at the leona alone she seems poor, but if we remember it's a team based objective game then it really isn't horrible? We just don't have any other good data to run with. Normally, that wouldn't be an acceptable performance, but if those death's were traded off for a power shift somewhere else then it's not a huge loss.