In theory it should have a flaw of weaker late game, but I haven't had a game where I picked it and the game was still competitive past medieval. For example I hit Renaissance on turn 105 in a game last patch, while several Deity AI had not reached medieval. That means tercio vs spearmen. I had a similar lead in culture, so I basically get free reign to pursue any wonder I want. Even if the bonuses stopped completely after medieval, WoT might be too strong.
There are several beliefs that don't scale that well, and WoT easily outperforms those. WoT provides 1,800 yields (excluding golden age points). The gain X yields for spreading beliefs would need to spread an absurd amount of times to match that. I think the percent beliefs are pretty close to the spreader beliefs in power, so WoT is the outlier.
300 of everything that early on puts you way too far ahead. It needs to be balanced if someone gets the bonus at turn 70 (which is very doable for civs with bonus faith). Also, consider synergy, if 300 culture grows my borders a twice and I have tribute, I'm actually getting 360 food/gold. If my capital grows 3 times and I have cooperation, that is another 21 of all yields (which could mean even more border growth or pop growth!)