I really don't have a side here, but when things don't make sense I do question it. Could you please provide the powder loads and expected MV for maximum MV for these 225gr loads?
From my Switft manual, the 225gr load for the .338WM uses 74gr of RL-22 for 2750fps, that is the maximum velocity listed. From the same manual the 225gr load for the .35 Whelen is 60.5gr of BL-C(2) for 2623fps.
Ok that is 20% less powder but it's also 5% less speed. Thus the .338WM will have 10% more energy and 5% more momentum. Add to this the increased sectional density and BC, it's hard for me to buy into this notion that the .35 Whelen gives .338WM performance with identical bullets.
Will there be more recoil with the .338? Of course there will, but I'd put that up to the .338 shooting considerably faster, that's just physics.
To be certain both are proven calibers and I'm not disparaging either. I also own neither of them. I have a .300WM and a .375HH. Having both of these, I just don't see a hole that either the .338WM or .35 Whelen fills, that my existing two choices already don't. And I'll shoot my .375 with 250gr bullets all day long, heck even my wife is starting to do that now. Go "down" to the .300WM and with 200gr bullets and I'll shoot even longer.