This is a hugely important point. My second traditionally published novel - The Irresistible Summons - went through a hugely difficult edit. I actually wrote this article explaining what was cut and why, and I stand by the fact that the 93,000ish word final version is better for having 16,000ish words cut out (and other sections rewritten entirely).

Even after this novel was published, one otherwise positive review said my first chapter (after the prologue) introduced too many characters at once. I genuinely appreciated that insight, and realised on balance it was a correct criticism. I have been a lot more careful with how many characters I introduce at any one time since, remembering that hilarious moment in The Hobbit when Gandalf fears he may overwhelm Beorn if he introduces all the dwarfs at once.