Power creep definitely had something to do with it, and the beef-up didn't just affect Paragon & Epic.
Heroic monsters actually have much better design as well - power wise. If you think the MV Displacer Beast is bad, you've obviously not seen an encounter with anything that immobilizes and storm shards (MM2). Storm shards do something like 1d6+6 damage and if you fail to move 4 squares on your turn, you take an additional 3d6+6 damage.
Did I mention they are level 4 artillery? Did I mention they are Monster Manual 2 and therefore nowhere near the update?
As for power creep, I can't help but laugh at that because I bet you didn't see a party that was the original (unerrataed) versions of things like the Warlord (Whoring Quickening Order and Relentless Assault), a orb Wizard Bloodmage, a Infernal Warlock multiclass Wizard with... BLOODMAGE, a Cleric whoring Righteous Smite (for the Warlord to hit with Lead the Attack) and a Daggermaster Rogue. I mean that right there is a party that slaughtered Dagon in 2 rounds.
Two rounds. Why? Because put simply it couldn't be challenged with monsters at the time, blowing through all encounters with simple at-wills/encounters (minding the Bloodmages were both Archmages, if you know how that ED works you'll know what happened constantly).
That party is more powerful than anything that has come after it. Easily. In fact, that entire party has been nerfed by errata in one way or another in multiple places. There is a good reason for that.
Whatever the /reason/, though, higher monster damage will lead to combats ending in fewer, bloodier rounds, as the PCs feel forced to pull out all the stops - or, if they don't, take tons of damage - which means fewer combats/day. Exactly the phenomenon the OP is noticing.
I am not disagreeing with this, I am just pointing out this is the way things probably should have been. Aggressive fast combats and not huge grinds against monsters that - quite frankly - might as well not have been there in the first place.
Personally, I don't get the idea that fewer rounds of combat is more fun. I like playing the game, I'd rather play through 6 rounds of combat than 2.
I agree, but with the caveat that grinding out ineffectual monsters with a billion HP for six rounds is boring. An intense 3-4 round battle that leaves the PCs badly bloodied and injured - but was exciting from round 1 and didn't lose intensity "EG the cleanup is actually just as quick" is far better.
Believe me, when you need 7+ rounds of combat to scratch PCs into bloodied, you're not having fun.
4e combats were tactically much more engaging.
They still are. I mean I seem to be doing perfectly fine with this if you read the
notes from my game.
So, encounters became tactical exercises, where round-by-round decisions mattered.
I 100% firmly disagree with this statement. There is no "tactical excercise" in engaging a group of creatures that will simply not be able to do *anything* to you whatsoever. The reason combats needed to go seven rounds was because the monsters would have no chance of bloodying an epic level PC without it. You had to artificially extend combat by abusing stun and dominate powers. Have you noticed with the increased damage the amount of abuse that paragon/epic monsters do with stun/dominate has disappeared? It's simply no longer required to make challenging fun combats.
in a round or few, but you were then left 'grinding' away at the remains of the encounter with your at-wills
No offense, but you sound like you didn't play a lot of epic pre-MM3. PCs would grind away with their at-wills ANYWAY because monsters weren't enough of a threat to bother using dailies on in the first place.
Believe me, if I got my PCs to spend dailies I was
pleased. It meant they were actually threatened for once.
I basically disagree with everything you wrote. I don't know how much epic pre-MM3 you played, but it was full of boring grinding combats that required immense preparation time and - hell I'll outright say it - just abusing monsters ability to chain stun/daze/dominate to be challenging. Having to deny a player their turn consistently every round so the monsters had enough time to scratch down their HP was absolutely horrible.
Nothing tactical about it either, because the PCs had won from the get go and no matter what damage was done - nothing ever felt like it mattered. Epic combat felt like a boring grindy thing you just did to get to the next level. To fight more of the same ineffectual enemies full of HP.
I've wrote about my experiences with epic tier both pre and post MM3. I would
never ever go back to pre-MM3 damage/power design if you paid me.