The reason the corners are lighter is because somehow they got less exposure. Now, I'm not an absolute expert on these matters, and so someone else may indeed know a *lot* more about it than I do and will chime in--but I do have fairly extensive experience printing, up to and including 4x5.
I think the most likely cause by far is the lens. 105 is not the standard focal length for 4x5--it's more suited to 6x7cm. Normally, when printing 4x5 you want to have at a minimum a 150mm lens. So, I think your instinct that the lens is not giving you sufficient coverage for the whole area of the negative is correct. (Especially since your 6x4.5 negatives came out fine--a 105mm lens has plenty enough coverage for that format, for which an 80mm lens would be the "standard" focal length.)
Another possible problem is making sure that you have the light source set at the correct distance from the negative. I'm not familiar with DeVere enlargers--I've always used Beselers--but especially if you're using a condenser head, it has to be adjusted to the proper height from the negative to ensure full coverage of the light source on the negative. If you're using a diffusion head, it's probably not so important, however.
As to your final concern--to get the most out of a negative, generally you're *always* going to need some dodging and burning. It really just can't be avoided, unless you produce that mythical *perfect* negative (but even if you do everything exactly right when exposing and developing it, just because of the way photosensitive materials work, it's not going to anticipate what you *want* the final image to look like and so parts of the image may--and probably will--still need some work).
If you're committed to using large format--which is really a brilliant, and very fun way to shoot (if you've got the patience and discipline for it), and still provides the ultimate in quality especially in terms of amazing tonality and resolution--then I would suggest that you get Ansel Adam's authoritative three-volume set titled The Camera, The Negative and The Print. If you use his techniques and master pre-visualization, you can come much closer to getting the negative that will provide (with a bit of work still in the printing stage) the image that you are striving toward--you can change your exposure, your developing technique, the grade/filtration of the paper you're printing on, etc., to get the kind of contrast and tonal range that you're seeking. Adams' pioneering and thoroughly systematic work on the subject will allow you take control of these factors.
But you're still gonna have to dodge and burn, most of the time!
