It may be the case that U2 are quite democratic and fight tooth-and-nail every step of the way, but I still don't think your point is valid. Just because it's a democracy doesn't mean you get a free pass to produce nothing, and solo artists like Bruce have to write all the songs themselves, without collaborators.
Sorry, it's valid. The solo artist makes the final decision. It's quicker to write on your own than collaborate. Also, there are fewer variables (families and other commitments) to affect the recording process.
If Edge writes a song, he has three guys, plus the producers, wanting to fiddle with it. If Paul Weller, or Bruce, or Ryan Adams, or any other solo artist writes a song, it is done. He has final say. He's the songwriter. It's his thing.
If Bruce was in a democratic band I doubt he'd be putting two records out a year. I have a feeling that if Bono made all the decisions for U2 SOA would have been out, that they'd put out records and NOT tour them. If Bono wanted to put out a record of ambient, chilled out "hymns", he'd do it. But because other people don't want to, he has to respect that if he is unable to convince them...and who knows how long the arguing goes on for. Because Adam is adverse to releaseing a record and not touring, every record they put out has to be filled with a particular type of song. If those kinds or songs aren't what comes naturally, it slows the process down. And the process has already slowed because of their age. How many bands their age put out records every 2 or 3 years? How many bands, period?
U2s breaks between albums are the norm for bands that have been around for as long as they have, maybe even a bit better. Some 2000-2012 stats:
AC DC have two albums
Rush have three, and and EP.
Tool have 2.
REM have 4.
Wilco have 5.
The Cure have 2.
Depeche Mode have 3.
ZZ Top have 1.
Primal Scream have 4, but only 2 from 2003 onward (same as U2).
Radiohead have 5, with three in the last decade, and 2 after 2004 (same as U2 from 2004-jan 2012).
U2 have 3. That's not so abnormal, is it?
Here are some solo artists:
Paul McCartney has 9.
Paul Weller has 7.
Bruce has 6.
Billy Corgan (basically a solo artist) has 6, plus a shitload of unreleased stuff and songs only played live.
Ryan Adams has 13, and that's discounting all the unreleased albums. He's younger, yeah, but if he was in a democratic band there is NO WAY he'd have released seven albums in five years, while recording at least six more unreleased albums during that same time.
Damon Albarn has 11 from all the different projects he's lead, and he could have called them all solo albums save "Think Tank." That's the freedom someone who isn't a band has.
Solo artists have more freedom in what they record, what they release, their work schedule, if and how long they tour for, and so on. The song is finished when they finish writing it, not after three other people take it and play around with it, adding and subtracting. They direct what the musicians do, as opposed to a band where dictating what bandmates play is usually problematic.
Also, it's not like they're doing nothing. They're playing gigs! They tour for a really long time. Their shows are really spread out, so they're on the road for a year and a half or two years. And then when they get off the road they probably want to take a bit of a break...though their schedule is basically a vacation with the odd performance thrown it, isn't it? And then when the break is done, the long process of making an album begins again.