Ok, let me just try to compare. Data points are the summer playoff rosters 2017 vs. 2019. I'll just try to bring up the data without further comment, as I'm kind of neutral on the whole "NA imports too much" topic. I'll list the imports by teams, and then summarize in the end. Also I'll show the "import-percentage" of each team. Source is lol.gamepedia.com.
Season 2017
C9 2017: Ray, Impact, Jensen. Ray and Impact shared toplane. (3 of 6 players were imports)
CLG 2017: Huhi (1 of 6 players imported)
EF 2017: Looper, Froggen, Gate. Gate was counted as NA resident (2/3 in 9 were imported)
Flyquest 2017: No Imports. 5 Players
Immortals 2017: Flame, Xmithie, CodySun, Olleh, Dodo, Unnamed Italian Player. Dodo, CodySun and Xmithie were NA residents. (3/6 in 7 players were imported)
Phoenix 1: Inori, Ryu, Pirean, Arrow. Inori was an NA resident. (3/4 in 10 were imported)
Dignitas: Ssumday, Chaser, Shrimp, Kean...