I played almost all these games (with exception of Book I and Gates to Another World) and don't remember beginning so rough like in IX.
I have two Might characters (Mercs looking for promos to Gladiator and Assassin) first use Spear and second is Blade focused, both have them at Expert mastery level. Both have Armsmastery at Expert level.

Even with Bless spam and average Accuracy of 21 they still miss 7 hits out of 10 (before getting Expert skill they missed 8-9 out of 10 hits).
What gives?

I know that there are NPC to hire and it looks like they are mandatory here (never used them in other M&M games) and they are barely better than my lvl10 team...

Hmm...it's a loong time since i played it so i am not sure if this is still true

I.Reading your post it's unlikly but Armor in M&M IX and X could give Accuracy
debuffs if you used armor without the right skills

II.
For M&M& the mechanic was
(15 + PlayerAttack*2)/(30 + PlayerAttack*2 + MonsterArmorClass)

That's should be 90% thc against a Brigandinerating and around 78% for Chainharness but then you have to take evasion into account and that is where the problem might be.
If i remember right they where several complaints about the changed formula for IX and X.
It was something like it changed the thc from 50% at even values to 43%, the default evadechance from 5% to 15% and made the dimishing return effect bigger so the PC's need values much higher then the monster eaderating to get decent thc's.

The Solution was to modding the formula, making a party that uses mainly magic as offence or fighting through..just raising the skill&Might untit it works.
But that was over 10 years ago, i couldn't find any of the old Sites or devposts with "official" numbers/statments...:(

Aside from this...i can only say that many people complained about the thc in IX and X, some guessed bugs and reported that sword hit much worse compared to maces with the similar thc..

Hope you find a solution, good luck

I found MM9 to be vastly different in real-time mode in comparison to turn-based mode (which OP is probably using).

Unlike MM6-8 (where turn-based mode is actually more preferable), in MM9 you have drastically higher speed and seem to hit much more often. I realized that when was fighting lonely Lich Lord (or something like that) and my party couldn't kill it at all - it was like super mega boss. But once I switched to real-time mode, I easily defeated Lich Lord as if he was made out of some harmless paper.