The difficulty you are describing assumes a user base of crypography pedants who make assumptions about third parties that don't matter to 99% of non-technical users (nor even technical users in many cases).
One example: you work for the American government, and you witness something very wrong, very illegal going on. You'd better be sure, when contacting Laura Poitras, that you are indeed contacting Laura Poitras, and not some counter-intelligence operative from the NSA.
And it has to work even if you don't have Ed Snowden's skills. Without reliable crypto the rest of us can use, people will get caught, arrested, tortured, killed blackmailed… just for speaking up.
Maybe we don't want reliable crypto to be widely available. Maybe we want to have mass surveillance. But that's another debate. (Personally, I'd rather have everyone to have reliable crypto, and I'm willing to make wiretapping impossible in the process.)
How to beat Laura Poitras publishing a public key all over the place?
Without forward secrecy, getting Laura Poitras' key will enable the NSA to read all past communications. They only have to seize her computer when it's still on, and the key is still in memory somewhere, or compel the poor journalist to give up here keys (possibly using that "non invasive" waterboarding torture, and justifying it with suspicion of helping terrorists).
Now if Laura kept the decrypted messages in her laptop, forward secrecy wouldn't do anything, but if she properly deleted them, it would be a shame if the messages were nevertheless at the mercy of the attacker.
As for key finding, well… the simple solutions do work pretty well. Snowden for instance didn't find Poitras' keys lying around on the internet. He asked someone he trusted would give him the right key.
It isn't real ambiguous.
For instance, Snowden had someone tweet a key fingerprint: https://theintercept.com/2014/10/28/smuggling-snowden-secret...
Hint: TOFC is a lot like what I described above, with the added usability that you don't have to type "yes" every time like a chump.