I understand the point your trying to make, but from a technical point of view what you say is absolutely not true.

One of iOS' fundamental security features is that all code that executes on the device must be digitally signed by Apple. This means that even if a vulnerability were to be found in, for example, Safari (or any other system software), the damage that vulnerability could cause would be virtually nonexistent, because malicious parties would be unable to use that vulnerability as a vector to install and run malware, as that malware has not been digitally signed by Apple.

Jailbreaking your device disables this most fundamental of security features. This means that if a malicious party found a vulnerability in the system software, they could go ahead and exploit that vulnerability to install malware on your device.

If you don't download any sketchy tweaks or forget to change your SSH password with it installed, you won't run into any problems.

This is bad advice. How "sketchy" software is has no bearing on how much damage it could be, or if it is malicious. This seemingly legitimate software package could be harbouring malware, and you wouldn't know any better. Case in point: An Android third party browser used by millions was secretly uploading users browsing history for years before anyone noticed. The only reason this spyware was found was because the developers were foolish enough to transmit the history to their servers in plaintext, allowing an intuitive user with a packet inspector to stumble upon this most egregious of privacy violations. If the authors of the software had taken minimal care when designing the software, by encrypting the data in transit, chances are that we'd never be aware of the spyware packages with this seemingly non-"sketchy" software.

The only way to be sure that software is not malware is if that software is open source. And if you're not a software engineer, you're going to have to trust others to audit the code, which is a big risk itself.

Ultimately my advice is to not jailbreak your device. It's the only way to keep it virtually 100% safe from malware.

If you must jailbreak, then install only open source software with large enough usage that you can be somewhat confident that the code has been thoroughly audited.

If you jailbreak and are installing closed source software, you really don't know what you're installing and if it is safe.