Quite right, the Hebrews citation argues against Calvinistic perseverance [which - my own argument here] is like unto the scriptures in their originals]. But it does stomp on the concept of the return of the Prodigal, a tenet which to the Calvinist hardly requires argument, but you can still point to the scriptural problems.
And while 70x7 is not explicitly soteriological, I would maintain that it does give evidence on how we are to take "as your Father is perfect" and support the Arminian stance on the Prodigal.
This when I have done I have not Done, for I rather like Sir [St] Thomas as well as the original twin [and what did they call his brother and which one was he?] Later.