"Here were some big problems with monsters in 1e. 4e seems to have the same issues, even though I don't know much about it" is what I got from your post, so yes, I can see how it could be seen as unfair to 4e.
Here were some big problems with monsters in 1e that resulted from some subtle problems in the rules that didn't really manifest themselves until higher levels. For example, in 1e monsters THAC0 advanced fast at low levels, and then slowed down at high levels - player effective THAC0 on the other hand advanced faster and faster (even progression + even progression of magical enhancements).
According to the original poster, 4e has subtle problems manifesting themselves at higher levels, so maybe you should look at things which don't differ that much between PC's and monsters at low levels, and things which do differ quite a bit between PC's and monsters at high levels.
As for criticals not being the problem, maybe that's so, but the OP claimed there were two problems (not one, as some others have claimed).
First, the OP claimed that at Epic levels, combats tended to go long.
Secondly, and I think equally importantly, the OP claimed that at Epic levels, combats tended to become predictable. According to the OP, the monsters stopped feeling like a threat.
Someone complained that boosting monster crits wouldn't help the problem but would make combats less predictable. I find that a strange complaint, given that the OP complained about the fact that the PC's never felt threatened and that the combat followed a very predictable arc.
Someone else has claimed epic solos differ from lower level solos by having x5 rather than x4 hit points. That seems relevant as well.