Anecdotal: Think I had a runaway Arabia (Difficulty 5, Continents) on another continent somehow explode on the tourism front, winning on 252 just as we were getting into Industrial (I had one tech + one I stole from them). Arabia started on another continent and seemed to have secured a solid lead in the early game. I wasn't particularly thinking (haven't played in a few months) and gave it (shared) Open Borders within maybe 20 turns of meeting. It was Influential to me before I even had a chance to not renew them (didn't think it was gonna skyrocket so fast, so didn't declare war to slow down the tourism, though it likely wouldn't have mattered).
I was trying Authority Huns (I rather liked the VP update to the Hunnic abilities/bonuses). I founded a religion and got the culture per follower Enhancer (Inspiration?). My social policies seemed to mostly keep pace with the non-Arabia civs, though maybe a tad behind (I'm not used to the heavy warmongering style - culture for kills 'n such). I didn't focus on guilds and popped my few Great Writers for culture rather than Great Works, but otherwise my infrastructure was fine. By the time I'd met Arabia I'd eliminated one civ and was out teching the remaining three on my continent.
I remember Cultural victory being nigh accidental a few times I played in the past, but not this fast. I remember Diplomatic victory was pushed back closer to when a Science victory is possible, so this seems... incredibly early?
Glancing at the Tourism screen, Arabia (at Turn 251) has produced 123,526(!) Culture, whereas the last holdout against their Tourism output has produced a mere 39,063 Culture (think I was around 33k, so lagging but not abysmal). My spy in Arabia's capital tells me that it was currently getting +79 Science/Culture from its trait, which seems kinda high.
I understand that part of this was just a case of a runaway civ, but I was pretty close to them in tech (6 policies behind, but expected when they produced -that- much culture). I kind of feel like there's too much tourism weighting towards incidental events and less on active focus of a civ (Archaeologists are a good example of needing to actively focus on it, like with the Diplomacy side of things). There's also less counterplay in comparison to Diplomacy. I'm not sure what the solution is, but something seems off with Cultural Victory mechanics/gameplay.