Does the OEM air filter "suck"? Why yes, it does. Like all air filters, air is allowed to be "sucked" through it. Otherwise, the internal combustion engine cannot work, and to tell the truth, there is only so much fun one can have sitting on the bike in the shop making "v-room v-room" noises.
(feeling a little playful this morning, forgive me....)
I've never taken the air box off an FJR and examine the throttle bodies for cleanliness. But I do know that in about 150,000 miles of riding FJRs, I've never had a ride ability issue indicative of having dirt in the induction system. Further as Ray mentioned, if you blow high enough air pressure through any pleated air filter, dirt will get through it. I do clean my air filter about every 10K miles, but I blow low pressure (about 30 psi) air in the reverse direction of the normal flow.
Still further, I would offer that your short and slow gravel/dirt stint for each ride is in fact contributing to your condition. I've followed other riders into the campground and other situations where we are riding slow on gravel/dirt. If it's dry, trust me - you are stirring up crap, and based on the location of the intake, that crap is absolutely getting sucked in. Not saying that is a deal breaking issue, the filter is doing it's job. Just make sure that your filter is sealed well into the box (film of grease is a great idea), and perhaps clean it out (reverse blow job) at every oil change. I replaced my air filter at 50K, just because I wanted to and I had one in my shop that I bought for my Gen 1 bike, and never used. You may want to replace yours every 25-35K. But I wouldn't buy an aftermarket filter. The bike just runs too dam good in OEM form - no point in throwing curves to the ECU.
Just my $0.02 worth. Money back guarantee if not satisfied.