The $999 SurPro3 looks to be roughly equivalent spec-wise to the base rMBP at $1299... add on the type cover and you're at ~$160 savings to the SurPro3. At that point, it really comes down to preference in form-factor and OS.

Same goes for the i7/8gb/512gb SurPro3 at $1949+cover vs a similar rMBP at $1999... the rMPB gets the edge by ~$90 but, again, they're so close it comes down to OS and form-factor preference.

And at the low end, the base 11" MBA edges out the base SurPro3+cover on specs (better processor, more storage) but I'd consider them close enough for general productivity and light multimedia work that you could buy on OS and form-factor preference. Compare the same 13" base MBA configuration and the SurPro 3 has the spec edge, but still fairly comparable.

I don't think either the SurPro3 or anything from Apple is going to win out on pure value at a given spec level. If you're buying either it's likely because you like the form factor, the OS, or both enough to justify the up-sell.