Even if the penalty is reduced for broadcasting an old state, it shouldn't matter if both parties have a watchtower. In the case of a broken/non-functional watchtower the loss of a lot of money would happen in both lightning and eltoo.

I agree that the decreased risk would probably result in more old states being broadcast, but maybe it's a good thing for a watchtower to be tested more frequently. It should also be easier to manage watchtower software in eltoo since only the latest state is needed so I wouldn't be surprised if lighter weight supplemental watch tower services started to rise up.