It's mostly that MM3 monsters have a combination of really good power design and really good damage. So they are more fun and interesting to fight, while MM1 creatures have just been left far too far behind in the past power wise. Redoing MM1 creatures usually requires updating both their powers and damage expressions.
Well Aegeri is using something called 'hyperbole'. Overexagerating to create an effect.
Actually no I'm not. Have you seen how many builds utterly destroy Orcus easily? Actually, Orcus isn't even a threat to any decent level 30 party that is remotely competently put together. I've actually ran epic solos like Orcus and they are nowhere near as effective as those that came later, like Demogorgon or Lolth.
MMI Solos are not absolutely terrible and fundamentally flawed at a base level.
Yes they are. They have:
1) Too much HP, making them very grindy and this is combined with their enhanced defenses enhancing the "grindy" feeling
2) Too little damage, so they cannot even generally threaten PCs anyway - especially because they often have
terrible action economy to face a party of 5 players.
3) Brutes are an absolute joke, because they'll spend all day stunned/dominated and dazed due to utterly miserable defenses and their attack accuracy isn't sufficient (something MM3 fixed nicely).
They might be for his game, because his game has players which might be overpowered or underpowered and too fast or too slow to fight against a MMI Solo monster and not produce a fun and exciting result for their game.
MM1 solos are routinely described as being boring grind fests, it's a common complaint and its why Wizards changed solo monsters HP (20% less) and defenses. This isn't just "My game" this is a general complaint that resulted in the fundamental maths as to how solos are designed. If this was just "my game" why were they completely altered by MM2? Wizards doesn't just pay attention to what I say, so it can't just have been me that noticed solos had too many HP, not enough damage and weren't capable of challenging a party of five PCs (not enough actions usually, or poor action economy).
Also considering that I can get lots of good battles out of solos I make myself, MM2 and MM3 solos - I feel the problem is easily with one particular kind of solo. Those that the games maths have outdated considerably. I currently run 3 games and I can't recall the last "boring" solo I ran that wasn't from the MM.
And the fact that Solos in MMI were playtested quite a while and said playtesters did not have nearly the same problems or issues with them (since, you know, after all, the game did get released!), tells us that what Aegeri says is not an empirical fact.
You seemed to have missed where the playtesters or Wizards allowed things to go to print that were immensely broken out of the bat like Cascade of Blades that was errata'ed within one week IIRC - meaning that I'm not exactly enamored with this argument. The fact is that solos have been the discussion of
numerous threads since 4E has been released. The most common complaints are that they are boring, grindy and unable to break out of repeated daze, stun and similar lockdowns. MM2 addressed this and then MM3 has really helped fix a lot of other issues. The lockdown issue is still there, but it's nowhere near as bad as on MM1 creatures.
That being said... now that we've had two years of worldwide playtesting, and bucketloads of additional supplements to expand the game in ways that those original designers of the first MM's Solos could not think of... is it surprising that some of the original stuff is not as good at producing fun and exciting results for some people as the newer stuff that's been released?
I mean, it's not like Wizards have changed
1) Damage
2) Hit points
3) Defenses
4) Number of powers
5) Increased damage while bloodied
Since the release of the original monster manual to make solos more competitive. Wait,
actually they did change all of those and for the better in every case.
But for everyone else besides Aegeri... there's no guarantee that what he claims is correct in the slightest.
I pulled this out of your first paragraph to respond to it last.
Here's a question for you:
If I am not right about this, why was the maths changed dramatically?
Noting that monster manual creatures are now
two iterations of dramatically changed maths behind. They are also behind on power design compared to MM2 and MM3 creatures. They are behind the curve in
every manner compared to "current" solos. If you honestly think that MM solos are fine, then explain why the purple worm is a good solo or for that matter, the Dracolich. Either one is a contender for
absolute worst monster in all of 4th edition.