You're right. The Splash mountain log flume is quite long, longer than most long flumes. If the show scenes aren't spectacular, the ride will absolutely fall flat.By all means then, gut the interior so it's just a concrete flume riding through dark steel hallways. See if most people still consider that to be remotely as fun.
The drop is fun and looks cool. It's not what gives the ride staying power though. If that was all it had going for it, relatively few people would be remotely as upset about this overhaul. The interior scenes are what makes the ride stand out and places it far above any other log flume out there.
When I first road it as a kid, I didn't have any idea that it was going to be a fully fledged immersive dark ride inside. I just figured it would be a prettier take on the log flumes i'd ridden elsewhere. I didn't know there would be impressive interior scenes with amazingly detailed sets and tons of animatronics with a narrative progression, and those were what made it spectacular and one of my favorite rides of all time. It needs those scenes far more than it needs the big drop.