Is it probable that every WRX owner at some point went over the 4,000 RPM by a few hundred or even 500 RPM's during the break in without a subsequent negative issue/consequence. No argument there.
However, to imply that all break in rules are to ignored by other forum members without any potential consequences is not prudent, especially based on how "low RPM's diesel motors" are being broken in.
Along with everything single manufacturer in the last few years, Subaru now has the capability of recording our top RPM's (and so much more on our cars' powertrain past performance parameters), and if the OP's or if anyone's vehicle has a motor and powertrain problem, especially if it is an expensive one to repair, and as an OEM can now point to a specific RPM violation of its Owner's Manual, they might deny that warranty claim. And if for example I hit 6,500 RPM twice during my break in period and my motor blew up at 400 miles, rod going through the block, a Subaru dealer is not going to go "wink, wink" and ignore my clear violation of their break in rules just because I bought a Subaru from that dealer, or whatever, and there is a high likelihood that that dealer is not going to replace my motor with a new or even a rebuilt one at no cost to me.
I owned three new 335xi BMW's and I know the rigor to which my motor's past performance, including RPM levels etc. were analyzed each time I brought it back for another N54 high pressure fuel pump failure -- as do you. About the eighth fuel pump failure, the Technician pulled me aside and apologized to me, and showed me an extensive print out of what detailed RPM and mega-tons of other info that had been downloaded from my car its ten hour overnight computer history download, telling me that all that data had already been sent back to BMW Germany for them to further analyze my motor and its problems.
Additionally, just as GM did two years ago, more and more OEM's are no longer allowing major warranty claim approval by a dealer, instead now adding a new position, called a Regional Warranty Approval Supervisor, to first review all but basic (cheap) claims. I even had a $150 claim on my 2015 Z06 initially denied by my dealership. I told them I wanted to appeal they denial, but they told me that their Regional Warranty Approval Supervisor had already been consulted and he too had also denied it. (I appealed the Supervisor's denial, and GM eventually agreed to pay for my warranty claim.)
Point is that OEM's are getting tighter and tighter on approving warranty claims due to "tighter cost management strategies," and telling clubWRX's members to ignore break in Subaru's rules, can and for some members will have consequences.