OKW panther doesn't really arrive quicker than Wehr. They both take fucking forever.
Cost to get Panther as OKW:
200/40+200/80+490/175=890/295
Cost to get Panther as Wehrmacht:
200/45+200/55+200/60+80/10+120/15+160/30+490/175 = 1450/390
If you don't use the muni to fuel conversion then the fuel price is comparable with the 66% income, but the manpower difference is huge enough to make it ridiculous to say it wouldn't arrive quicker for OKW.
They have different armies supporting their tanks. The OKW panther also has 5 levels of vet, but Ostheer has cheaper repair, doctrinal stuff like free smoke, more supporting vehicles etc. They're different armies.
Cheaper repair like the free repair engineers around the tech building? Or cheaper repair as in having 320mp sturmpios that at vet2 with minesweepers actually have three times faster repair than vet0 (or two times faster than vet2) ostheer pios?
Free smoke!? I wish I had that.
That said, I don't really care either way since it's a slight accuracy change.
Accuracy is a huge deal for a unit with bad scatter and long range like the Panther.
Do you know the stats for the command panther?
Command Panther has the stats of the Ostheer Panther and gets smaller veterancy bonuses to its own stats, but the aura improves per level.