My Experience with Rakan so Far. (The bad parts)

Overall, Rakan has high Ap ratios on his defensive utility that often go to waste due to him having to build tanky to survive his insanely risky playstyle. Unlike ranged supports, you take a lot of damage as a consequence of your kit. You're always either throwing yourself into the enemy team, or throwing yourself into the same dangerous situation as an ally in order to protect them from it. He is especially vulnerable to CC, which can totally flatten any attempt to engage with W and R, getting you killed in the process. His passive is unreliable, but helpful when you time your W with it. His Q is short and slow, and blocked by minions. It's difficult to hit aggressively in lane for sustain, and puts you way out of position to poke with which usually results in you taking damage from the attempt to undo it. Stray minions will block it in teamfights. The delay on W can make it tricky to land. E is pretty short when not used on Xayah, and is crucial to actually getting your heal to who you want to get it to in a teamfight, AND for getting out. You rely on it so heavily for the mobility that really getting the benefit of the shield too is difficult. R doesn't always CC everyone at once, so any follow up CC has to be times after you get everyone closer together rather than near the start. I think it's better used overall AFTER someone's engaged on a group, and the enemy team's blown their CC. It's good at turning around a fight, and helping clean up too. Not the most dependable initiation tool though.

You do a lot of what other supports can do, but you trade safety and reliability for mobility and scalings, which doesn't seem like it's always the trade you wanna make on a support. You don't really even get to abuse your scalings due to how you have to build to offset his playstyle.