I find Pokorny very interesting, because I am interested in IndoEuropean
languages outside Germanic. You say that IE is an "imagined" language;
I would prefer to say it is "reconstructed." Good scholars are aware
that their hypotheses are just that, and hardly anybody would expect
to find, if we had a time machine, some group of people speaking exactly
what is reconstructed for IndoEuropean.
On the other hand, there can be no reasonable doubt that the main stock
of words in the IE languages goes back to common ancestors, and we have
a fairly accurate picture of what those ancestoral forms must have been.
We can even be fairly confident about the conjugations and declensions
of IE, in general terms.
For me, it would be disappointing to leave the etymology of an English
(or Old Norse) word at the oldest recorded form in Germanic (usually
Gothic), when it is clearly possible to go further and link up with the
other families in the IE group.