re: Mearls
Er, looking at Iron Heroes, I get the distinct impression Mearls has ALWAYS designed his fights more like an action movie where the environment plays as big a part as does the actual combatants.
re: Encounter Design and Solos
I think what a lot of people might be doing is the following.
They have a level 5 party and it is the climatic encounter with the BBEG (thus a level+4 encounter, namely a 2000 xp budget).
The DM could use a level 9 solo by itself, (white dragon - 2000 xp) but a "better" encounter would be a level 6 solo (blue dragon - 1250 xp) and a couple of level 5/6 monsters to fill out the xp budget.
I'm thinking the latter encounter would be much more satisying and not as well boring as the "let's surround it and slug it out" former scenario. Again, this _IS_ how the MM actually lists all the Solo monster encounters. There isn't one entry where a Solo fights by itself. From the weakest solo (white dragon) to the strongest solo (Orcus), not one entry IIRC recommends a Solo fight by itself.
re: Using at-wills first or at the end.
It doesn't matter the order in which the PCs use encounter/at-will/dailies since it will take the same number of rounds. What it DOES matter is how many round the monster will be at its bloodied state.
Personally, my group has pretty much restricted their big guns to AFTER the monster is bloodied since many of the monsters get more dangerous when bloodied or weaker all of which make their encounter/daily powers more effective.