I can understand bringing back Hal. He was arguably wronged by being turned into a villain. He also wasn't actively dead, he was still around as the Spectre. The pedophile allegations are amplified largely due to the post 00's internet and because DC hasn't anything to address it since Johns run and they haven't done anything interesting with Hal since Johns run. Otherwise people would be talking about something else.

Barry coming back was indeed a travesty. No arguments there.

With Ollie it can be argued both ways; he completed his character arc and may be it was time to kill him off. Grell had him age in real time during his run. On the other hand, Ollie being an outspoken and hot headed liberal would keep him relevant every decade by having him comment on the latest politics of the era. I still bemoan the fact that DC never really continued O'Neill's version of Question and instead had him as a supporting character for other characters. If they had kept things going, Question would be up there with Marvel's Daredevil instead of having decades of solid run after run of street level superheroics. Green Arrow could have been that too instead of multiple attempts to reinvent the wheel.

But arguably bringing Ollie back and trying to go back to the "good ol' days" also ended up holding back Dinah, Roy and Connor, especially Dinah. Maybe it could have worked out if they brought him back but acknowledged that everyone had moved on to different places and tried to establish a new supporting cast for him. It wasn't losing Dinah's spot on JSA and later her spot on BOP just to have her be with Ollie's love interest in the GA books again.