There are many different arrangements of the tiers that could be made. The one you suggest wouldn't be my preferred arrangement, but there's nothing particularly wrong with it.
However, I don't think the problem with Epic play in 3e and 4e was to do with them not having the right arrangement of the tiers. IMO there were two issues, one with game design, and one with support.
In both 3e and 4e, the complexity of the game increased with level, and never really stopped. (In 3e, this manifested as the game becoming extremely mathematically complex. In 4e, it was more an issue of juggling huge numbers of options. IMO, 4e had the edge here, though I wasn't a fan of either.) As far as I can tell, this was largely a matter of the designers making sure they got the game 'right' at the early levels for release (since that's what people would play), but deferring the later stuff... only to find there were insurmountable problems tucked away in the design. (Needless to say, I was more than a little disconcerted when WotC said they were doing the same again with 5e - that will almost certainly lead to the same problems.)
Because of the complexity of the systems at these levels, there was a greater need for support. However, there were also fewer people playing, meaning that WotC couldn't justify providing that support. This, in turn, turned people off playing at those levels, further reducing the incentive to support those levels...
That leads me to one of two conclusions:
1) WotC should design the game only to cover those initial 10-15 levels that people actually play in numbers, and that they themselves can reasonably support.
Or...
2) WotC should work really hard to make sure that the game does not become inherently more complex as it goes up in level (or, at least, no more than it absolutely has to). This will mitigate the need for support, that they cannot guarantee to provide. If this then leads to more people playing high levels, this will justify them providing support, and at that time they can consider introducing more complex Epic modules. But they should work from an initial assumption that they're not going to be able to support it, and so build the game to work without.
IMO, of course.