Dunno for the elefant but JT can deal with infantry, quite well in fact. I had couple of infantry squads 2 shots by JT
If you move, it can't change targets. It's on a cool down. It costs muni. It can be a fairly unreliable ability - there are time s it just collides with something else. Usually craters.
You literally had to stand around for it to do that. I've never wiped a squad with it, because people either move or retreat. Then the damn thing is on cooldown and you can't do anything.
Generally it boils down to this - After you've tried to upgrade your fusiliers you can possibly squeeze in a barrage or two. You can keep doing it but you'll lock yourself out of your doctrinal arty.
So no, the JT isn't a thing that I would consider to use against infantry. Have you ever tried it? It's a pretty terrible ability. It might work if it were a timed damage toggle but if you move out of the barrage area to either charge it or retreat then it's pretty much done because it can't follow up any shots.