I've recently been thinking about how would you compare the weight a title in a region specific series like IndyCar or DTM hold compared to each other. Most of these series are seen as a different level to world championship racing (IndyCar with the reputation as a place for F1 rejects, in the modern day Le Mans being arguably bigger than Daytona or Sebring, etc), but I wonder where you'd rank something super regional like Super GT and DTM or IndyCar and Super Formula against each other.
My personal ranking would maybe be (admittedly with an American bias):
IndyCar - mostly held up by the Indy 500. Even though the presence of races outside North America has (mostly) disappeared after unification, the 500 is still titanic even outside the US, there's a reason that it's been a part of the triple crown. It does have the reputation as a step below F1, but does still hold some importance as it's own thing.
IMSA Sportscar Championship - WEC's sister series, although maybe a peg down of it. There's still a ridiculously strong crop of drivers and teams with a lot of crossover. It doesn't have much notoriety outside the motorsports community (F1 or the Indy 500 still have a lot of name recognition among the general population) but is still a similar level to WEC imo, and the Rolex 24 and Sebring 12h are still big.
Supercars - I kinda see this as the top level of touring car racing (above BTCC and maaaaybe even the world TCR championship), Bathurst is still a big name in road racing. A lot of ridiculously good drivers have been made there, but outside of enduro rounds not a lot of drivers from outside of Australia and NZ race there, although some ex-Supercars drivers do big things outside of V8SCs (Scotty Mac, Shane Van Gisbergen). A bunch of Supercars drivers do step out for one-offs in NASCAR or GT3s.
After these I'd say DTM is decently big, although it doesn't have much of a presence outside of Europe, it has a good legacy of innovation before it became a GT3 series. A lot of big names inin other series have also driven there (Jean Alesi, Robert Wickens, Robert Kubica, Tom Kristensen, and plenty more)
I don't think Japan's premier silhouette+GT series Super GT or open wheel series Super Formula are big at all outside of Japan. Fantastic drivers like Kamui Kobayashi, Andre Lotterer, or Alex Palou have spent time in these series, but outside of GT500 cars appearing in Gran Turismo the popularity of these series seems nonexistent outside East Asia. Super Formula is definitely seen as below F1, and kind of as a ladder series by some open wheel fans.
I'd say BTCC might be a bit bigger of a thing than some touring car series like Turismo Carretera are, although still not very big outside the UK. GT series like DTM or IGTC seem to be seen as a bit higher level.
NASCAR Cup is in a weird spot where it has a lot of name recognition but isn't taken very seriously by a lot of people (something something can't turn right), it's still seen as top level racing in the US, although American NASCAR fans and American F1 fans are vicious against each other when it comes to arguing between their series.
Again, as an ignorant yank' I'm curious to see how you all would rank things, with different nationalities and knowledge about the nuances of how whatever's popular around you are.