Leonas legendary skins are pay to lose.

Are you going to provide any evidence or give us an example of what you're talking about? As of right now there's no substance to this post, nobody has any idea what you're talking about. I also think you might be in the minority because most Leona mains I come across love the skins.

Any proof of it being janky?

youd have to test drive it. Leona is already janky to begin with, but these skins exaggerate it by so much.

Base skin Leona is... Slow, gigantic in terms of unit collision, very telegraphed.

Solar/Lunar ecliplse Leona pretty much doubles her size, which drastically decreases the speed in the appearance of her movements. Exaggerates her unit collision problems. Her autoattacks are wack. and her Zenith blade is even more telegraphed.

The only true Leona skin is Project...

There are genuinely skins that give you a disadvantage. Project Vayne is a good example, as her E is significantly more telegraphed, and makes it easier to avoid getting pinned.

I'm not sure Leona's skins have a similar effect, but I'm actually going to go into practice mode and see if I notice any difference.