The enclosure means a lot to final performance, but it cannot negate speaker specs. Fs is a perfect example. The Fs of a speaker affects EBP, impedance rise, etc. So since fs affects EBP, its a big factor in whether or not a speaker should even be ported, let alone affecting the tuning freq.
Can you tune below fs? Yes, definitely, but there is a trade off. Fs is a function of suspension compliance and moving mass. The enclosure will affect compliance (over all compliance), but the speaker's suspension (and thus, fs) is not ignored once placed in an enclosure.
It is true that distortion increases as cone excursion increases, but assuming the excursion stays within the xmax of the driver, how noticeable that distortion change will be is debatable. BL optimized drivers will display virtually no audible distortion changes based on excursion differences, again assuming it stays within xmax.
Sure, DD9500's and Kicker L series drivers have won SQ competitions. But usually SQ judging is done at relatively low volume levels (like mid 120's) where the differences in design types between a stiff suspension, heavy moving mass like most SPL designs, will not be nearly as apparent. Try having a SQ competition at higher volume levels, and subs designed for a more linear response will be more able to show their advantages over a design like the 9500. Nothing against the 9500's, or even L series, but to suggest they are capable of SQ competition winning performance is to suggest they are an end-all be-all design that can perform equally as dominant in the SQ or SPL lanes... is over simplifying the situation and distorting reality. This is also true of the Warden.
There were a few other points in this thread I meant to address, but Ive forgotten them now and am too lazy to go back and look. //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif