It´s absolutely the same and 100% accurate if you just want to now your own damage/performance. The only thing what can make it inaccurate is when you do the wrong comparing like use different times/time cuts OR if you calculate your stuff wrong. I admit it´s a lot of work though analysing your video and calculate stuff. It´s an option if you have some free time, can´t ask someone to parse you and really want to know with who you are up to/what dps range you are in(or basically how good you are for real or how your build does compare).
Actually you don´t even have to be super accurate in what damage/dps you EXACTLY do if you don´t have the time or motivation for big analysis, if you just compare your recorded rotation to others in their logs(same runtime ofc) and it is identic, you are already solid - the rest is about finding out/comparing with others how and when to use your buffs, which don´t show in the logs(the increased damage portion from it does show up though). Ofc gear makes some difference too, but in FF14 everyone is more or less equalized very quick sooner or later anyway.
It´s nonsense. If you compare, you do it with the same content, same class and the best players and there are A LOT of dungeon entrys in the rankings. I admit, that other halloween like expert dungeon for example is kinda messy, but knowing all mechs etc is a part of getting good/better.
It´s the same for any other type of content. It´s not like raids will be easier or will have less going on, lol. Whatever content you compare, you compare it with the same class having to handle the same shait. The reason why you can´t keep up with the same rotation of that player is up to you to find out though.
I really hope arcadion raids will be parsed more than dungeons, sure then it´s the better option. But if it will be like 1 log every 10 runs, it´s not enough for me personally.
Still, dungeons are still a competing thing... just watch how many new logs there are in the rankings every day.