Prone to Breakdown makes a bit of a difference, but not all that much.
Consider that your opponent will usually try to keep attacking your vehicle until it’s destroyed. Once your opponent gets that first disruption on it (most likely from the rear) they will keep hammering on it until it’s destroyed. It’s very likely they’ll continue to hit the rear defence, now 5, each turn meaning you’re not going anywhere anyway; Prone to Breakdown becomes irrelevant.
However if they manage to score two hits the Elefant has no chance of avoiding damage, while the Jagdtiger at least gets a 1-in-3 chance of avoiding damage if it has cover. Now it’s true that if you’ve put your Jagdtiger in a bad position your opponent can simply leave it alone now; try to avoid that. Otherwise the Elefant is much much easier to destroy, and it still has bad AI dice and -2/-2/-2 AT dice compared to the Jagdtiger.
often doesn’t make much of a difference:
makes much o
Prone to Breakdown may seem bad, but I’ve seen more often than not, that it doesn’t make a difference. The opponent targetting the unit will keep hammering away at it regardless; as long as he keeps hitting it will be disrupted