For OS, exchange rates have gotten a lot worse since The Dark World came out, so Ragnarok needs to make significantly more in local currencies to match The Dark World's OS number in dollars.
Ragnarok is in a very similar position to GotG2 when compared to their predecessors. Exchange rates for The Dark World were pretty much the same as they were for GotG1, which is a lot better than they are now. TDW and GotG1 also made a very similar amount OS, with $438M for TDW and $440M for GotG1.
Many people thought GotG2 would increase a lot from GotG1 OS, and it actually did in local currencies, but exchange rates really held it back. If GotG2 had the same exchange rates as GotG1, it would have made about $100M more OS. Exchange rates are a major factor here, and it shouldn't be overlooked when you're using The Dark World as a comparison.
We shouldn't be shocked if Ragnarok did similar OS numbers to GotG2($474M).
Ragnarok has one trump card up its sleeves for OS numbers compared to TDW though: China. TDW is the lowest grossing MCU film in China in the last 6 years by a pretty wide margin: it made $55M in China while all other MCU movies since The First Avenger(2011) have made at least $85M+. If Ragnarok can make about $100M in China, that could give the OS numbers a nice boost, and a similar increase from its predecessor(similar to GotG2 -> GotG1) in the rest of the OS market would then get it to about $500M OS, a milestone only 10 superhero movies have passed before.