Like I said, I actually like his voice, he has his own sound and a lot of swagger that fits perfectly for the music but that doesn't mean he has great range. Billy has his place, so do Lemmy and Araya and Snake and any number of other guys, doesn't mean we have to play up a technical vocal skill that doesn't exist.
Most of the highs in that thread are single screams, not really his actual singing voice. The lows are stretching things too; spoken stuff like that example in Hatred's Rise shouldn't count (and it's funny that song be mentioned because the vocal melody is pretty much taken straight out of how he did Scorpions' The Sail of Charon). Most of the songs mentioned don't point out specific moments though so I can't say for a lot of those. Also, it's worth considering that you can't really compare highs from his early years and lows from later years; if his overall range went lower in pitch, it cancels out.
EDIT: And thrash generally isn't about singing range either. I don't know who I'd pick as examples of good range tbh. Russ Anderson had really improved from Forbidden Evil to their pre-Distortion demos, but he lost that pretty quickly. Maybe the second Toxik guy, he can definitely get way up there but unlike Sanders it's not all just shrieking and he can sing in non-dog whistle registers too. Oh, Erik AK has to be up there, probably Realm's Mark Antoni too for that matter. Chuck Billy doesn't really come anywhere near any of those, and obviously that's not his thing anyways.