Fun fact: Your Signal messages are saved sever side forever, even if you have self-deleting messages turned on. You used to be able to see them load up and then disappear on the desktop clients that hadn't been synced in a while. People complained (b/c WTF?) and Signal's "solution" was to have it work the same way under the hood but just hide the "deleted" messages with a loading screen so it wasn't as obvious. Fun, right?

Having said that, no, I don't think it's ever pointless to delete your chat history. It can only help, and even if it's on a service that keeps another copy lying around, deleting it still removes at least one copy of your data.

If we say there's no point in fixing issue A because issue B exists then everything will always stay broken. It's better to fix what we can and avoid using non-private services for private things going forward.

My bias: I did secutiry audits for large companies and got to see their architechures. No, I won't say who or leak any details about how their systens work, but I can tell you that it's not always kept server side forever. Yes, even in America.