Did not know this, but suspected as much from clues. Reason I do it here is mainly because here is where the game refers one when asking for feedback.
On the whole I agree completely (except possibly about the probabilities). Easy to misunderstand my point really. I prefer the large party format on the whole. I have played all the currently released adventures all the way through with all but one character (the monk is lagging a bit), mostly with large groups (5 or 6) except in the beginning.
The bit about feeling well equipped I agree on, but I note that it is in general just that, a feeling. Think about it.
You might have characters and items that cover most situations, but there is no reliable way to make the skill meet the need except by luck. It is just as likely that your rogue runs into a magic puzzle (and fail) while your wizard runs into a pit trap (and fail, in pain... ...probably together with the poor monk, who can't use his skill to stop the stupid wizard dumping both of them in the hole) as the opposite. And since the pit trap gets shuffled away, there is no real point counting on the acrobatics there next turn, since it might now be at the bottom of the deck.
The one exception to this is, of course, location specific needs. Those can be rather demanding and really benefit from specific talents.
The main issues here is the fact that, in general, you either loose due to time or win so completely it's almost sad. And that the difference between these two is often one, or possibly a few, die rolls somewhere past the mid-game. Succeed and you curb-stomp the villain (two successive combat rolls of expected average 30+ usually suffice), but if you fail there is virtually no chance to recover.
(E.g. 8 turns left, encounter villain with (you think) reasonable preparedness (having found it with spells and moved the right heroes to the right positions). Then miss one simple temp-close (1/8 chance), which makes you not close another by banishing a card. Then miss a pre-battle check by rolling less than 5 on 2d12 [a 1/24 chance]-> bury virtually entire hand, including weapons/spells -> loose fight -> get hit with a 4 damage hit that hits everyone at location and may not be reduced, then loose 2 card from the blessings deck and loose track of where villain is with 7 turns left on tracker and very few cards in hand for at least 1 other hero... optionally, burn almost every booster every character have to avoid getting smashed down -> same situation, except that now every character has used most blessings they had on hand and you have one turn more, still... good night)
The extremely limited turn count makes it all about luck more often than not, since there is no real room to recover from a failure. And this... is at normal difficulty... (and yes, the above example actually happened)
But I used the phrase difficulty multiplier, and it is on heroic and legendary that this problem actually becomes aggravating. Since even minor increases in roll difficulty makes above scenarios a lot more likely (because of the nature of multi-die probability curves), even ignoring any scenario special rules like "each time you find a foe, manage a difficulty x or get cooked for y damage" or similar. Several of the scenarios are virtually unplayable with a large party at higher difficulty in my experience.
But on the whole my peevishness is not really caused by changes in difficulty (2 char parties are mostly boring, im,nsh,o).
My problem is one you pointed out. That it becomes, for all intents and purposes, different games.
This was the point which I suspected I would get most general agreement on. I'm glad I seem to be right about that at least.