Well, Thunder is good on Hydration Lapras, due to you probably having a rain setter. Perfect accuracy is better than 100 accuracy for sure. The problem is, if you don’t have a rain setter, Thunder is super unreliable. Thunderbolt, under normal circumstances, will never miss. Usually, not missing most of the time is better than it always hitting with special conditions. Of course, Thunder has more BP, so that can mean the difference in some battles. Reliability can also be a deciding factor.
Edit: Either slap Rain Dance on it, get a Pelliper (or any other Drizzle Pokémon) and use Thunder, or just go with T-bolt. But if you really want to use Thunderbolt in the rain or Thunder in... um... normal weather, go ahead, I won't stop you.
Hope this helped!!! :)