The Gump Sox won 93 and 95 games in his two years here. He then won 170 and lost 154 in his two years in LA. 358 wins in 4 years as a manager, nearly 90 wins per year. He never had a losing season as a manager. If that's not enough for people to stop arguing that he was a bad manager, nothing will ever be enough. Right? Farrell is in his 7th year. 3 winning seasons, 3 losing seasons, one exactly .500 season. Decidedly average in terms of outcome. Less so when considering the talent, and of course his in game moves.
Re: your second point, I agree, there is a ton of mediocrity out there and very few difference makers. But that doesn't mean you should keep Farrell, IMO.