Unfortunately this wouldn't make taking Old Ben to R9 any more appealing than it is now. I'd almost call it a trap.
Old Ben's unique works best when he is the first ally to be defeated. But because Old Ben is a durable and easy to avoid unit, that's difficult to do. This problem becomes more and more apparent the higher you take him. Thus a R9 Old Ben is almost guaranteed to be the last one to fall. It does not matter how many stats you give if there's no one to give them to. This Touch Up completely ignores this problem and thus end up practically doing nothing.
If that was all, then it would be a pretty pointless but ultimately harmless Touch Up. But unfortunately it also disregards what I consider to be one of Old Ben's greatest strength as a tank: His high Defense stats. If you compare character base stats on SWGOH.gg, you can see that Old Ben has the 5th highest Armor and 12th highest Resistance among all units in the game, including GL's. That is impressive given how old of a unit he is, especially Resistance since he gains none of that from his mastery. By comparison his Health and Protection, even with the R9 bonusses, are slightly below and slightly above Average respectively. He's one of the few units on which Def% primaries could actually be quite good in the right circumstances. Yet this Touch Up encourages you to ignore that unique strength for the small chance to have other stats transferred. I find that quite wasteful.
I'd recommend boosting allies defense before he is defeated, rather than boosting them when he falls. Something like: "At the start of battle, all other allies gain 75% (doubled if all allies are Jedi or Rebel) of Old Ben’s Defense until the first time Old Ben is defeated."
That would make it so other allies are more durable until Old Ben falls, thus making it more likely he is the first to fall. Not to mention, since the bonus goes away when he is defeated, you don't want him to be defeated too quickly either. Would this make Relic 9 worth it? I'll admit, maybe not entirely. But it does help and makes investing into him more worth it.
For fun you could also give Luke Skywalker (Farmboy) guard until the first time Old Ben is defeated, if he is an ally. That was what Old Ben was doing after all and could help lift Luke up a bit. Thou he will probably need his own Touch Up for that as well. Anyway these are my thoughts on the matter. Hope it was useful.