I think that Brumbär should have some major advantage in AI capability over the ostwind when you take into the account that they are in different tiers. Currently they both have the same shock AI role and same weakness to AT and TD. One could argue that ostwind is even stronger option now due to AA, not being as micro intensive and it is able to flank stuff due its rotating turret.
Arguing that brummbär shouldn't be able to outrange AT with ability because pzwerfers exist is like saying Zis guns shouldn't have barrage. "If you need indirect fire then mortar is your choice."
It has its advantage in form of field presence. Brumbar outranging Atgun proved to be OP because the only counter left are Tank Destroyers. Tanks Destroyers that the same vocal group of Axis fanboy complains about their supposed over powerness and want to nerf as well. ATgun are still one of the counter to Brumbar so it is normal that the brumbar doesn't have an ability to counter them from safe distance.
Imo T4 suffer more from heavy tank meta still in use in 90% of games than being weak. Ostheer T4 is still the way to go vs Allied premium medium tanks and heavy elite infantry play.
Ostwind going on par with the Brumbar is a problem of Ostwind being too good, not the brumbar being bad, Brumbar 2 or 3 shots any squads and that the maximum it can do as per balance standard.