Bob,if it's ok with you,i'd like to put in my $0.0002 on this...(loose thoughts,more questions than any certainty...).
I'd guess that the feeling of massiveness comes from there being SO much thickness in the sides of the eye.
That,and the parameters of that eye are sure odd...I could almost say that it's a possibility that it was a discarded forging,unsatisfactory in some way...Except,the axe have been worn down in Some kind of service....(btw,is that an over-laid bit that is worn clear through,by chance?Down to soft iron?Or is it just the sharpened edge reflecting light-colored-like?).
The iron that was used for the sides is of a rather poor quality;almost certainly it was the remnant of a wagon tyre(about 1/2" thick,minus forging losses?)...One can see the weld seam running clear down the middle of the poll(thank you for such decent photos,btw).
Such material,1/2",is not really sufficient thickness for that size tool....Not an US axe,a Scandinavian one-maybe,and as a matter of fact by how the blade is forged slightly narrow in front of the eye,it is reminiscent of Sweden and the like(GB still forges like that today).
Inverse taper of eye is also from that neck of the woods,apart from above.
So,if i had to find fault with material or workmanship,i'd say that the iron was of a very insufficient refinement.Also,the welds don't look so hot....(Not that it's their Job to look hot,and the tool Did remain integral through what appears to be a long ordeal,but them Are lousy welds).
So,so far-the axe was thrown together out of poor stuff,quick and dirty one may say,with this tiny eye,and a very significant poll...(for an axe that size-won't you say?).
One possibility is that it was initially a forge tool(set-tools,having to transmit the blow,normally have very heavy sides of eye,also,eye don't need to be very big,the handle is static,just for holding onto).
Maybe a hot-cut for copper sheet?Some other lighter-duty forging action?(fishing here...

....)
No mushrooming like most struck tools,but a smart smith never did let that stuff build(naturally).
And the last point of strangeness/uncertainty:Judging by it's construction detail and material,it was never ground at the original manufacture.However,it bears signs of Severe grinding,even maybe cutting...Was it used in some weird manner,where it got all beat to...,on Top(and bottom)?...That i can't find any plausible reason for...
Sorry for such pointless,long-winded essay...Neat tool,whatever it's fate was.Hand-forged tools have lots of soul about them.