This is why I will never understand the arguments over ratings between the various Arrowverse shows as an indication of which couples/characters/shows are "most popular". Ratings vs. sales are dependent on a variety of factors. A show with lower real-time ratings can end up with higher DVD sales where the inverse may be true for another. All of the Arrowverse shows target their own specific niche and clearly viewers have different priorities when it comes to viewing habits, time constraints, disposable income, etc., so the infighting is useless. That said, while I do think the sales of Arrow are likely having an impact as to why it has lasted six seasons, I wish the network would consider ending it next season as the show has always had a huge problem of recycling/repeating old storylines. To me, that's a indication that your arc is played out and you need to plan an exit strategy. I strongly suspect that's why Arrow ratings have been declining faster than the norm as well. I know personally I've been fairly bored the past few seasons and only skim the episodes out of loyalty and love of specific characters.
Guggenheim & Co. have always said they planned a 5-year show to coincide with Oliver's backstory arc, and even at that, it felt as though they sometimes had to stretch out the plot to fit that timeline at the sacrifice of quality. When it became clear that the network had no intention of canceling Arrow, I think the showrunners didn't really know where to go next so they hurriedly introduced a bunch of new characters that nobody really warmed to in an attempt to continue the gravy train. While I don't think most general viewers hate the newbies as much as many people here do, I do think they are a lot more disposable in terms of audience loyalty so focusing on them so much (especially last season when the ratings really started their slide) hasn't really done the show many favors in retaining viewers when the stories are weak.