The three spool architecture should have produced a lighter weight engine, but the RB211 was the heaviest engine on the B747.
Someone once told me that it was only heavier because the opposition didn't include, in their basic weight specs, engine parts that RR considered standard (possibly cowling, reversers, etc). GE cowling, I believe, hangs off the strut, rather than the engine.
The RB211 may be quicker to spool up (once running), but it takes significantly longer to ground start
