To be fair, in the case of something like a Linux ISO, you are only a tiny fraction of the target or you may not even need to be the target at all to become collateral damage. You only need to be worth $1 to the attacker if there’s 99,999 other people downloading it too, or if there’s one other guy who is worth $99,999 and you don’t need to be worth anything if the guy/organization they’re targeting is worth $10 million. Obviously there are other challenges that would be involved in attacking the torrent swarm like the fact that you’re not likely to have a sole seeder with corrupted checksums, and a naive implementation will almost certainly end up with a corrupted file instead of a working attack, but to someone with the resources and motivation to plan something like this it could get dangerous pretty quickly.
Supply chain attacks are increasingly becoming a serious risk, and we do need to start looking at upgrading security on things like the checksums we’re using to harden them against attackers, who are realizing that this can be a very effective and relatively cheap way to widely distribute malware.
The end result is exactly the same.
The difference is that you can install an iso on a computer without an internet connection. The normal iso contains copies of most or all relevant packages. Although maybe not all of the latest and most up to date ones, the bulk are enough to get you started. The net install, like the name suggests, requires an internet connection to download packages for anything except the most minimal, bare-bones configuration. The connection would hopefully be nearly as fast if not faster than the iso and be guaranteed to have the latest updates available which the iso may not. While such a fast connection is usually taken for granted nowadays, it is not always available in some situations and locations, it is not always convenient, and some hardware may have difficulty with the network stack that may be difficult to resolve before a full system is installed or may require specialized tools to configure or diagnose that are only available as packages.
In almost all cases, the netinst works great and is a more efficient and sensible way to install. However, if it doesn’t work well in your particular situation, the iso will be more reliable, with some downsides and redundancy that wastes disk space and time.
Things like windows updates and some large and complex software programs and systems often come with similar “web” and “offline” installers that make the same distinctions for the same reasons. The tradeoff is the same, as both options have valid use cases.