Great fielding teams can make $5M starters pitch like $10M starters. I've had teams with $25-$30M spent on the pitching staff lead the league in pitching.
But, good fielding, like everything else costs money, so it's hard to cover every spot in your lineup with exceptional fielders who can also create offense. So it's a balancing act.
I can tell you from personal experience that a great defensive team with a $40M-$50M pitching staff will struggle to score more than 2 runs a game.
And it's not just about errors, range is key as well. For example: a 2e4 Second Sacker is reported to be the equivalent of a 1e22.
Look at this team for an idea about what a truly good defensive team looks like (not saying it' a great team, just that it's a great defensive team):
https://365.strat-o-matic.com/team/1776595And you need to consider EVERYTHING including: catcher throwing errors, passed balls, catcher arm, outfielder arms, pitcher hold ratings, pitcher WP & balk ratings. All of those things go into building a good defensive team.