This is actually good advise. I am running ProxMox on a very old PC (3rd Gen i3 with 8GB of ram), and I really like it, which is why I wanted to move it to my server Box instead.
But now that you mention it, I may be better off keeping my UnRaid box as it is and use is as NAS/Storage exclusively and then build a good box to run everything else from ProxMox.