That link is built by a Diamond player; and it's a general idea of what's strong and not strong.
If your logic is correct, and by that I'm speaking from my view; why isn't Bard T1, or even God Tier? He's shown a lot of promise in the global champion series, especially in LPL and LCK, where they're actually really good with the kit.
It's because the meta doesn't exactly favor supports making big plays because Assassins and burst champions fuck him over.
Exactly. She's godtier because she counters the meta. People are playing assassins, people are playing to snowball. If Lux snowballs, she snowballs hard. That's it though. If she plays in a lane against less assassins or close ranged ADCs, she'll won't do AS GOOD as she is now. She's only God-tier as long as the meta stays this way. Sure her W and E could use some damage tweaks, but once the meta favors more tankier or more direct all in fights, she's going to be up there.
Her weakness's are very noticeable. If she misses a Q, she's gone, she can't combo as well. She misses E? Oh well. Her W is built for utility and that's that. She has trouble winning against extremely hard engage ( Think Naut/Malphite etc ) and she can't handle being on the backburner unless she's unable to choke under pressure.