I swim a few hundred miles annually…fresh water, salt water, and pool. Longtime triathlete. All my swimsuits are Lycra®/spandex…the same as all my cycling shorts. But the reason I wouldn’t like doing the ride-swim-ride in cycling shorts isn’t because of the padding absorbing water while you swim. It’s because of how soggy padding would feel after the swim when you get back on the bike. Yes, the padding absorbs water. But in the water it’s mostly neutral weight and you’d hardly notice it while swimming. Of course you wouldn’t want it in a (swim) race. But it’s not like you’re towing a boat behind you. You’d be more efficient in cycling shorts than if you were swimming in a baggy beach swimsuit. I think the simplest solution is to wear a spandex swimsuit instead of cycling shorts. Depending on how long the ride is, you really probably don’t “need” the padding anyway. And it’ll likely dry out on the ride home. Also…I’d go without the towel.
Dan