Dragonsbane
Proud Grognard
PC's attacks are typically stat + proficiency. That ranges from +4 or 5 at 1st level to a maximum (before feats, items, and other wierdness) of +11 even at 20th.
Well +5 from a stat, +6 from proficiency is +11. But a 20th level PC would have a magic weapon, lets assume +3 max. Then some feat or fighting style, such as Fighter / Archery, another +2. Thats +16 right there, without a spell or other boost such as Bard inspiration.
I had been considering adding the monsters proficiency bonus (or half of it) to AC to make up for this number gap, as I read so many high level PCs crush on monsters.
Bounded accuracy is a strange and inconsistent beast!