I think they are thick so they have enough meat to be universal or account for a large amount of variance in eye size / shape.
In regards to weakening it. Im not sure, I guess it must weaken that part of the handle a little bit.
However my take on it is that the part within the eye/just under it is inherently the weakest part as its the thinnest and has the kerf / slot cut into it.
IMO a shoulder underneath the head is not going to help prevent the head snapping off. The weak part is above that.
Whats important is having the kerf the correct depth, so the bottom of the axe head snugs up on part of the handle shoulder that is still complete (does not have kerf cut that deep).
Getting fatter just below the head is not going to make it any stronger where the handle meets the head which is the weak point. You get strength there by having the head seated down far enough and the kerf cut to the correct dept (i.e the kerf should not run right to the bottom of the head, there should be some solid wood within the eye at the bottom.) kerf / wedge should only go about 2/3 into the eye of the axe, and the bottom should be seated on solid wood, with no slot in it.
In regards to weakening it. Im not sure, I guess it must weaken that part of the handle a little bit.
However my take on it is that the part within the eye/just under it is inherently the weakest part as its the thinnest and has the kerf / slot cut into it.
IMO a shoulder underneath the head is not going to help prevent the head snapping off. The weak part is above that.
Whats important is having the kerf the correct depth, so the bottom of the axe head snugs up on part of the handle shoulder that is still complete (does not have kerf cut that deep).
Getting fatter just below the head is not going to make it any stronger where the handle meets the head which is the weak point. You get strength there by having the head seated down far enough and the kerf cut to the correct dept (i.e the kerf should not run right to the bottom of the head, there should be some solid wood within the eye at the bottom.) kerf / wedge should only go about 2/3 into the eye of the axe, and the bottom should be seated on solid wood, with no slot in it.