There is really not that much junk mail in the traditional mail, in my experience. Probably it varies place to place, but it's much MUCH less than what I get in my gmail.
My experience is the opposite. I'm constantly getting junk mail at my home with no filtering, meanwhile gmail does a great job blocking unwanted emails.
I suppose it depends on how you count volume. I maybe get 2 or 3 pieces of "junk" mail a day, along with bill/renewal/etc. associated paper (most of which is handled electronically), and few other letters and packages. Certainly I get way, way more than that in email whether outright junk or the loosely-related result of being on countless industry lists, etc.
I get 10's of actual unsolicited spam emails per day that want me to click a link and run an exe, or buy Canadian drugs, or give bank account details so they can send me millions, etc.
I will say that Gmail seems to catch almost all of that historical sort of spam for me. But I get another 50+ emails per day (not counting those that are dumped in my spam folder--probably because enough people reported them as spam) that are various marketing because I once had a badge scanned at a show, someone bought a list of scanned badges from somewhere, I entered an email to download a doc I wanted to read, a PR pitch because I sometimes write for publications, etc.
None of this is exactly spam and I sometimes go on an unsubscribe binge (and report as spam anything without an unsubscribe) but it's still a flood of mail.
Are you a homeowner? I do get some legitimate mail, though always from companies that already sent me a digital bill I paid by auto-debit anyway, that just refuse to go paper-free even though I'm throwing away all the paper they send me. But the overwhelmingly majority of my mail is unsolicited refinance offers, just as the overwhelming majority of my SMS texts and phone calls are people claiming they heard I want to sell my house.
If communication wasn't worthless before, flooding money markets to drive interest rates to permanent zero finished killing it.
At least with email, most of it gets automatically filtered, though it is also quite annoying there when every company or contractor I have ever purchased anything from ever feels the need to send me every day updates on everything happening with their business.
I think amounts of different types of spam one gets is variable, but it's trivial to ignore email spam. Even a smaller amount of spam in your snail mailbox has some negative side effects over spam in your email mailbox.
* An overstuffed mailbox tells burglars you're away
* There's more waste involved - it mostly goes to landfill (unopened)
* An overstuffed mailbox leaves less room for legit mail (most email services are good at creating a focused mailbox, so there's not the same signal to noise issue there)
* ID theft is probably easier from intercepting a preapproved credit card application than being able to hack your email password