>
> Yes, there is a need: to show the umlaut of the a-stems and u-stems
> in the s-ablative -es (*-a-(s)is), -uis (*u-(s)is).
>
Why can't the -es "ablative" of a-stems and the -uis of u-stems be
analyzed as *-a-i-s and *-u-i-s, respectively? Apparently a well-
known Etruscan sound change is *ai > *e(i).