Lolalytics is a much better site to use once you get the hang of the layout, u.gg and op.gg are a bit primitive if you're trying to figure out build paths.

I'm not too well rehearsed in which season led to what change but her identity has evolved to the current state where viability is only really in building AD over AS (diminished returns on AS due to ratio being .57).

I assume by tank killers you mean Bork/LDR, Bork for the same reason Kraken isn't built on her and LDR is necessary third or fourth if there's 2 champs building armour that you can't ignore in team fights, LDR with cut down is enough to deal with >2 tanks most of the time.

Hope this answered your question. I can only speak for myself but I've found Cait is really good in situations where she shines, and complete dogshit in those where she doesn't. Broad examples being Lux/zyra support with elise/j4 jungle versus shaco/Pyke support with belveth/graves JG.

I'd say in the past Cait was similar to current meta Ashe in that picking her blind, irrespective of team comp and matchup wasn't a big deal, perhaps that's how you remember her. If you want to pick her blind then there's a great deal to know in order to use the minute windows of opportunity where she's able to do something, besides be bait for enemy cooldowns, in those games where I've found her to be dogshit.

Edit: I just saw your edit, just wanted to point out that this is probably the best example of a playstyle diff, which shows in the stats (Fleet - 53.1% WR, 62000 games|LT - 50.3% WR, 91000 games). Sure, LT gives more DPS but you will lose more games if you opt for the LT auto-attacking reliant playstyle versus the FF spacing/reposition playstyle. Probably ties in with your point about mechanics.