William Dunbar’s Lament for the Makaris (Elegy for the Poets), written about 1505

Okay by 1505 it was Middle Scots, not Middle English (I was thinking of it as earlier).

Now the two verses you quote don't illustrate it, but my problem with rhymes was that he not only rhymes Latin mê with English long e, as expected, but also with what is now a final short or long -i vowel:

And feblit with infermite;
Timor mortis conturbat me.
...
The flesche is brukle, the Fend is sle;
Timor mortis conturbat me.
...
etc. with many other examples throughout it

(Southern English: short /i/ in infirmity, long /i:/ in sly -- this was of course before the Great Vowel Shift moved /sli:/ to /slai/.)

If Middle Scots was simply intermediate between Middle English and Modern Scots English, this is odd. What I suspect must have happened is that final /i:/ had moved down to /e:/ by Dunbar's time, and was later restored by southern English influence.