I think brumbar can be more effective against allies blob. Right now i enjoy using ostwind more. Brumbar rng aoe and slowness make it more susceptible to 60 td.
You should try holding fire and use attack ground instead of auto fire, it can be really rewarding. Need a lot micro though.
That kind of nerf is acceptable because no one gets a brummbar to fight mediums. Brummbar is performing the same role as soviet kv8, it doesn't need to have some penertration like this. Now it has good chance taking down snared mediums and that seems confusing to me.
I do think after they nerfed the range and armour of brummbar, it should at least have 960 hp like panther. But no better penertration than t-34, the deflection damage is enough to let grens to snare the flanking medium.