Just for context: I'm basing much of what I'm about to say on Lvl4s and Incursions, since they're the bread and butter of highsec PVE.
Many (myself included) tend to say things like "PVE should be more challenging."
There's a counter-argument that floats up from time to time that goes something like this: "CCP shouldn't waste their time making PVE harder. Any scripted content is ultimately farmable; people will just adapt and in 2-3 months they'll be back to farming risk-free again." The argument is then (most likely) used as a crutch to prop up why dev time should be spent on pvp aspects of the game.
While painting the back side of my house today, 20 foot up a ladder, the light bulb went off: I don't necessarily want harder content, as in, more difficult to kill. What I wanted was a sense of satisfaction; a sense of being clever.
PVE difficulty is really a 4 legged animal. One leg is inbound damage that the Fleet must mitigate. Another leg is outbound damage (aka "Fleet dps") that's used to kill the bad guy. The third leg is enemy hit points that the players must overcome.
At a basic, basic level, these three legs determine if the Fleet is going to be successful. If Fleet dps can eliminate the enemy hit points on the field before the inbound damage starts killing things, then nobody floats home in a pod. Simple math.
The last leg, and perhaps the one that's most missing in EVE is the Satisfaction factor. It's the nuances of the combat system that allow you to do clever things to punch above your weight class. It's the things that take experience, skill, and coordination. It's the unsaid things that a Fleet of well-practiced comrades can do if they can predict what their wingmen will do, so that they're in position and ready to take advantage of it. It's the difference between say, 5 guys randomly pulled off the street to play basketball against the LA Lakers. Both sides probably know the basic rules - get the ball in the basket. But one side knows the moves, knows the game, and is well rehearsed. They don't simply play the game, they play as a team.
"All right, guys, uh, listen. This is a blues riff in "B", watch me for the changes, and try and keep up, okay?" - Marty McFly
A good Fleet ought to be like a good band. Individual members ought to be skilled enough in their own role, but also adaptable and watching for the changes.
Once upon a time, in another hack n' slash MMO, 3 guildies and I would set out to do crazy things. We wanted to see if we could kill 10-man content with 4 of us. We ran 5-man content with 3. None of us were pimped out in gear. We didn't even use voice coms. But each of us knew our character class well enough to hold our own. We had played together enough that any of us could read the situation and react appropriately. We laughed when we died (and oh boy did we die gloriously). But in the end, we were generally successful, and we were proud of it.
This kind of situation isn't one you'll find often enough in EVE. People play for isk/hr and min/max their exposure in terms of ship loss.
It's that 4th leg of the horse that EVE's PVE content has been often missing. The game system rewards players who fly solo or multi-box. It doesn't reward players who put in the effort to play as a team. It doesn't reward attempting to take on content you arguably shouldn't.
Until the 4th leg is fixed, giving us "harder" content will still cause the horse to run with a limp.