I'm not sure I believe that about foam. Now, I race 1/10 and 1/8 off-road nitro rc cars. And the track is of course dirt, and as the day goes on, and the track gets used it dries out and creates very dusty situations. It would be a dust level of that of the desert races. Now, that dust is extremely, extremely fine, so we run foam filters on our cars. We even run the foam filters on our cars when we decide to run them on the beach, and if ANY sand gets in the engine, it will completely destroy the engine. These engines are not cheap either...a race level engine costs around $400, and a long life on these engines are 8 gallons for a big-block until you have to rebuild them. Then since these are usually expensive, high-end italian race engines, rebuilding them can cost up to $300! Now, obviously, these engines aren't cheap, so we do the best we can to keep them running. I personally run a 2-layer filter on my 'buggy' and a 3-layer on my 'monster truck'.
Now, K&N does in fact make little air filters for our rc cars, and yes they look cool, but are the ABSOLUTE WORST you can buy. They let waaay too much in, and with those filters in dirt, you're very lucky to get 1 gallon on a big-block.
But, the foam filters attract a lot of dirt, especially with the filter oil, so you have to clean them usually every run or two while out at the track.

Now, I understand that real cars, and these rc cars are waaay different...(I could tell you anything and everything about rc cars and how they work, but dodge rams...not so much, lol.)
So I'm guessing that if foam filters really are as bad as you say, then the foam they use on cars isn't has fine, and is more pourous than on our rc filters...

 

Some Duramax diesel owners did a very complete test
using the SAE laboratory tests
on how various air filters did...both for filtering and for flow restriction.

The website is now offline, but the old webpages are in Google's Internet Archive at:

http://web.archive.org/web/200412082...011/SPICER.htm

Even if you skip all the words
and just look at the pictures and graphs
you can learn a vast amount about air filters
at the above link

 

Yup, that is why I am content to run the paper filter (Purolator) with the new air assembly I have, instead of a K&N. It might flow a tad more with the K&N, but the performance with the paper filter is very good, plus it is a better filtering medium.