GTC-FK
difference between qualifier 1 and 8 = 0.164 secs
difference between qualifier 1 and 16 = 0.241 secs
GTC-Pro
1-8 = 0.088 secs
1-16 = 0.434 secs
Can-Am
1-8 = 0.109 secs
1-16 = 0.177 secs
F1
1-8 = 0.131 secs
1-16 = 0.243 secs
It's a little harder to tabulate the closeness using laps, but this one example should suffice.
This is the top part of the combined results by lap total after the Can-Am Sub-Mains.

Just ten laps covers the first 16 drivers and the first three drivers have the same lap total to the tenth of a lap! The first eight drivers are spread over just 2.8 laps.
What other genre of slot racing besides Retro has such close competition?