Is that just a convenient argument for the occasion, or do you believe that your point holds more generally? If the latter, then Gilbert is above Boonen too?
Yes, for me he is.
It's an opionion of course, many can disagree.
Boonen is a great champion, one of the greatest of all time on cobbles, but too linked to the hyperspecialization period of cycling in 2000s.
I consider more riders that can win on more terrains.
To win in Roubaix and at San Sebastian, at Flanders and to keep wheels of the top climbers on Ghisallo and in the same time be able to challenge sprinters in Sanremo as Gilbert did in 2005 , 2008 and 2011 reserve much more appreciation from me that win 4 Roubaix.
Boonen won 7 monument but only 2 types + WC + podium on Sanremo
among the other very important classic 5 harelbeke and 3 Gent-Wevelgem (all cobbled)
than other many minor classics
Gilbert won 5 monuments but of 4 types + WC + podium on the remaining monument (Sanremo).
Then won many of the most important classics after monument but of very various type (amstel, strade, fleche, san sebastian, paris tours).
We have also to say the Gilbert won 11 stages in all 3 GTs in all terrain, also mountain stages.
Boonen 8, lacks the triple crown of stages. More than Gilbert has a green in TdF.
It's not a sin in my opinion to say that Philippe had something more as a rider than Boonen.
Boonen actually out of cobbles and sprint (but only in the first part of the career, then his sprinting ability became much more weak) did not exist.