Yeah, the ATDU is kinda meh in PvE.
The only thing that makes it even remotely worthwhile is the PISH round, and with the PISH nerfs you need to have Sabrina to make the PISH useful. Once you get Sabrina and you use a mostly PISH loadout you end up with a tank that is above average in terms of capability (it's tanky enough to do the job, the PISH round deletes ammo racks for massive damage). Even then though, there is really only one way to make the ATDU work well, but other MBTs (in their "top" configurations) are still just straight-up better than the ATDU in most situations.
The problem with the ATDU is that it is a one-trick pony. It's entire viability as an offensive tool (because most MBTs have similar capabilities as defensive tools after 0.33) is based on the PISH round. If the PISH round works the ATDU is a viable offensive tool, but if the PISH round doesn't work the ATDU suffers. It could be possible to make some changes to the ATDU to pare back the damage dealing capabilities while improving the defensive capabilities (e.g. increase side armour, reduce rate of fire) that would make the ATDU feel a bit more different from the other MBTs, but they would be in almost the complete opposite direction of the 0.33 balance changes (and as a result, we're probably not going to see it). The other option would be some nerfs to other MBTs (my.com have said that they were trying to make a MBT meta with the 0.33 changes) to bring them in-line with the ATDU, but I wouldn't bet on that happening either.