Kokou no Sousei isn't really a stream map.
The majority of the map is 1/2 notes, which are actually singletaps, unless you want to stream 120BPM. The map still contains a couple of 1/4 notes, and in the 5* version you get them more frequently, but if you're refering to the 4*, the map is like 98% singletaps.
AR9 on high BPM (220+) means a higher than average object density, which always results in a harder to read map, which is usually the main reason why people aren't very good on Saten's maps, or most older maps tbh.
So, if you really want to improve on maps like Kokou no Sousei, Worldwide Choppers etc. etc. then I'd advise you to play older maps that are more focused on circles and not so many sliders.
Some of Djpops maps are very good practice, but obviously playing all of Saten's maps helps you improving at his maps because his mapping style doesn't change all that much over the years.
TL;DR
Learn to singletap, and get fast at it. Stamina comes over time if you just play enough of these maps everyday. Play old maps with lots of circles.
Good maps to get good at Saten stuff:
Worldwide Choppers:
https://osu.ppy.sh/s/137377 (nomod and HT, lower AR occassionally in the editor for density, use HT if nomod is too fast) It sports pretty much the same "stream" patterns and sudden jumps and snaps.
Sacrifice:
https://osu.ppy.sh/s/40671 Asgard:
https://osu.ppy.sh/s/27712500 Tortures:
https://osu.ppy.sh/s/291155Utage wa Eien ni
https://osu.ppy.sh/s/7385Luv Letter:
https://osu.ppy.sh/s/40071The Creator:
https://osu.ppy.sh/s/41242EX-Termination:
https://osu.ppy.sh/s/50181Wahrheit:
https://osu.ppy.sh/s/53923Kyouki Chinden:
https://osu.ppy.sh/s/59025Dark Worlds Lament:
https://osu.ppy.sh/s/64631 (240BPM with HT lol)
Zetsubo Plantation:
https://osu.ppy.sh/s/86009Darkness:
https://osu.ppy.sh/s/79838Freedman:
https://osu.ppy.sh/s/108529Timefreeze:
https://osu.ppy.sh/s/158023Lone Digger:
https://osu.ppy.sh/s/454079Raijin:
https://osu.ppy.sh/s/16792Megalovania:
https://osu.ppy.sh/s/387700Packet Hero:
https://osu.ppy.sh/s/404910Highscore:
https://osu.ppy.sh/s/332532Hades the Rise:
https://osu.ppy.sh/s/33911Ghost Rule:
https://osu.ppy.sh/s/413117Pony Glitch remix:
https://osu.ppy.sh/s/49739Installation:
https://osu.ppy.sh/s/185927Masterpiece:
https://osu.ppy.sh/s/12483Taketori Hishou:
https://osu.ppy.sh/s/22276While the Saten maps look very simple, people often underestimate how hard they are to read and think they just lack the speed, aim and stamina for them, when often times they just can't read dense maps like that because todays maps go decimal AR9 already at way lower BPMs.
Just keep practicing it and you'll see progress quickly. Getting perfect and 100% consistent at these is incredibly difficult, though since the map is basically 100% consistent in its difficulty and strain, so don't be disappointed if you still miss on them even after months of practice. It's considered one of the hardest nomod maps for a reason. (Same with WWC)
Source: I have like a bajillion on Saten maps and WWC and got pretty good at it through all of the means and maps mentioned above.