The screw-up was that they picked a fuel that's not dense, and thus doesn't have much impulse per volume, and then picked a narrow tank diameter (8.4 meters)
That isn't exactly a screw up--you can't beat LH2 as a fuel. and 8.4 isn't as narrow as Falcon heavt, the EELVs, etc. Delta IV is the narrow beastie. But if you will recall, Ares V was going to be a 10 meter core, before the folks pushing ULA's agenda got it killed. Still, there is nothing wrong with a tall LV, and two DIRECT-ish Block IA Block II launches will allow for a lunar return--if it is supported.
Now frankly, if I had my druthers, I would push for something like Nexus or AMLLV--but that's not going to happen anytime soon. I'll take what I can get.
Now I think you might have called for wider LVs (that wouldn't fit in the VAB at any rate.
Here is a diagram showing how many RL-10s it would take to do the job of the original five F-1s
Now I don't think you want to try that with balloon tank construction.
Now I actually don't have a problem with wide vehicles, but that would cost a lot more than SLS right now--and may wind up being a global project. A global-lifter would be something to be planned out 50-100 years from now, with each nation pitching in.
I have this notion of a ring station made all in one piece but serving as a wet stage LOX tank near the base of a vehicle on ascent, with a superlightweight high volume hydrogen bullet nose that would be discarded, leaving the more sturdy ring tankage with spokes and all pre-built as a wet stage. This might be a cycler in its own right.