not sure how it is like in 1v1, but Jagdtiger is probably one of the most OP units in 3v3 and 4v4
Even though I don't play those big games, I believe you are right, as most of these maps are too small for such a number of players. But in 1v1 with its extremely limited mobility, I guess ISU got a lot more viable against OKW now, as you can try to avoid the JT and just wipe his infantry where the JT is not present. If OKW goes for a JT, there won't be much other armour around, maybe a Luchs or a Puma, but they can be handled even with HE shells and your other units.