I had one a few years ago that built an unbelievable size nest - the pair could barely squeeze into it cos the roof was in the way....
not had one like it since - but have a couple with nests the size of yours - and some with barely a straw in - one last year with half a dozen 6 inch nails and nothing else
can't comment on how well they might have done as I don't make notes on how big their nests are (maybe we all should)