If anything those comparisons actually makes Arrow looks worse than The Flash.
TV Ratings have been dropping sharply every year all accross the board since 2016, wether it be the Networks (ABC, NBC, FOX, CBS, CW) or the Cable channels.
On top of that, The CW keeps losing affiliates every single year.
Arrow S4 & S5 ran respectively :
- S4 : from October 2015 to May 2016 - S5 : from October 2016 to May 2017
The Flash S4 & S5 ran respectively:
- S4 : from October 2017 to May 2018 - S5 : from October 2018 to May 2019
And yet The Flash still manages to get similar ratings to Arrows with a 2 year gap for each season.
Just take all the above factors in consideration and let that sink in.