It’s not that the handle is going to rot, it’s that there’s zero shock absorption. The fact that it doesn’t have a replaceable handle probably means that it’s for ceremonial purposes, not fighting. Hitting another sword with it would be exhausting and painful.
I doubt that "shock absorption" would have been a problem.
This kind of sword would not have been used like a hammer.
The wavy pattern on the bronze handle would have ensured a firm grip even with a sweaty or wet hand. I have some Japanese Tojiro kitchen knives, which have stainless steel handles with a similar pattern on the handle, and they are more comfortable than most of the knife handles made of wood or plastic, especially when used with a dirty hand.
So based on this experience, I do not believe that such a bronze handle would have been a serious disadvantage, even if it is possible that the sword was purely ceremonial.
Nobody would have parried with a sword, except in desperate situations, because of the risk of breaking the sword or damaging its edge. That's what the shield was for.
However you have a valid point that anyone wielding a sword had to resist the shock of a successful parry with the shield done by the opponent.
For thrusting movements, I do not believe that such a bronze handle would have been worse than any other handle, because it is unlikely to have been more slippery.
Only for cutting movements you are right that a handle wrapped in leather or cords should have been better at absorbing shocks.
The reason I bring it up is a (minuscule) amount of personal experience: I've had the chance to practice/play fight with a replica bronze sword & shield against an opponent. We were expressly forbidden from parrying with the swords and it surprised me just how physically demanding the parries were against the shield, largely I think due to the ringing. Regaining control after the impact of the sword was hard.
That said, the craftsmanship of the sword I used was nothing like the one in the TFA and it didn't have a handle cast onto the blade, nor such an intricate design. I don't know how accurate the shield were to the time period (one was leather bound, the tower shield was not) but they didn't have metal rims and shield bosses.
