So I get that for the PCs 'to hit' math should work out to roughly 50%. So most PCs have a to hit bonus at first level of +6 to +8 (vs. AC) and typical monsters have ~16 AC at level 1. So that's 55% at worst and 65% isn't that uncommon - +4 for stat, +3 for weapon/class, the all-too-common Expertise.
Why is the monster 'to hit' so much higher?
Typical PCs (ignoring some outriders like light-armour users without a AC stat) range from 16 to 20. A first level monster typically has an attack of +6. That's 55% at best, down to 35% for the poor sap attacking a defender (Paladin, anyway).
Even discounting extremes, that's still about 60% for PCs to hit, and about 45% for monsters.
I'm a sad individual, how's that for an opening, if you check my sig you'll see the kind of thing me and my players have been up to- cataloguing every action (particularly combat) throughout KOTS, and now on Goodman Games Sellswords of Punjar. Connection rates are as follows, and this is for hundreds of attacks-
KOTS
PCs Level 1= 62.21%
Monsters= 55.29%
PCs Level 2= 64.5%
Monsters= 47.57%
That's quite a leap at Level 2, I want to see if this is sustained in other adventures- the truth is at Level 2 (and every other even Level) the PCs get another +1 To Hit (at least, sometimes +2 with their main weapon after a FEAT) and often get their hands on a +1 Weapon or Implement- it's a big jump. KOTS, imho, doesn't account for this- the encounters plateau, they get no harder, its not until the PCs are on the second level of the Keep that they increase in difficulty...
PCs Level 3= 61.72%
Monsters= 53.03%
Overall for all KOTS
PCs= 63.37%
Monsters= 52.21%
Sellswords of Punjar
Actually I'm still in the maths on this one (see sig), but its a lot closer than in KOTS, the PCs are hitting approx. 7-8% more than the monsters.
There are stats for every encounter, and I always make mention of the connection rates- in some (a few) encounters (particularly in Sellswords) the monsters connect just as often as the PCs (just), obviously you've got to remember that the PCs generally walk into a fight with the bad guys having more HP than them (discouting Healing Surges), in Encounter Level +3 and above the Monsters can have up to four times as many HP as the PCs. If the connection rate was the same for both (and damage done similar) then the PCs would just take a beating everytime and would be unable to sustain multiple encounters.
Personally, as a DM, I am fond of hitting the PCs with multiple encounters- I think twice in KOTS I combined two encounters which required the PCs quite simply to hit or die trying- titanic clashes (when used sparingly) that my players loved.
In Goodman Games scenarios imho this is much more prevelent as Encounters are generally much smaller, and much easier to overlap; if you check the Sellswords sig I think it's the third encounter the PCs get involved in- starts as a Level 1 Encounter (with 5 Level 1 PCs), by Turn #6 it has become a Level 5 Encounter, by Turn #8 Level 6 and by Turn #11 Level 7. As I say I don't do this all of the time (sparingly) but as a DM I'm aware that the PCs hit more than the monsters do, have plentiful Healing at times, and often hit hard- I'm also aware that they love these dynamic do-or-die encounters.
One last thing, regardless of connection rate, PCs die- at least that's my experience in 4e, and not just in encounters like the one mentioned above. One PC died in KOTS (McGyver the Dragonborn Paladin Level 1- best Defences in the party- failed three Death Saves), and so far in Sellswords there have been three deaths (Skamos Tiefling Wizard Level 1, Scurvy Dwarven Rogue Level 1- both failed three Death Saves & Corrin Halfling Paladin Level 1- again best Defences in the party, reduced to negative Bloodied HP).
My point is if the PCs don't hit hard and often then there chances of survival (over multiple encounters) would be much reduced- obviously that's just our game but we're playing published modules, mostly as written.
Cheers Goonalan