You might ask yourself, why pick J4 support?
I thought that too until I picked him in support for the first time.
My first time playing him, I picked him as a troll pick but then I saw the potential he had as a good support.

your E is amazing because it's a good poke and once you're level 2 and you upgrade your Q, it creates a field between you and your flag where enemies can't come (or else they get knocked up)
it's also great for your ADC if they're an ADC that revolves around auto attacks.
the poke part is amazing for spectral sickle.

your Q is good because of the armor reduction and because you can now knock up enemies with your E and you can escape sticky situations with the EQ combo.
also: if you time your E Q correctly you can still dash while CC'd

pretty good for slowing enemies, also gives you a small shield.
also it works well with font of life.

J4's ult is really good, you can ult on enemies to stall them, so your team can get kills etc.
imo your ult works great with large aoe abilities (like miss fortune's R for example) your ult makesit so that they can basically not miss it and it's a free kill (or they waste flash and you can kill them later)