Do SaaS founders who write their own homepage know which line is unclear? NO.
Most founders doing their own marketing can't see the weak line on their own homepage, because they know what the product does. Every sentence reads fine to them.
I think this matters because a marketing plan is built on that text. If the homepage says "the all-in-one platform for modern teams," any plan built from it inherits the fog. You end up posting content about everything and nothing.
So I'd test one thing first: take the homepage, pull out the lines a stranger couldn't repeat back, and fix those before planning any channel. I haven't proven this works. It's a position I'm reasoning from.
The best case against it is that some founders get traction with a vague homepage because their distribution does the explaining. A warm audience doesn't need a sharp line.
Where I'd guess the advice stops working: if you have no traffic yet, a better homepage changes little. You still need people to land on it.
For founders here who've rewritten their own homepage: which line did you find was the real problem, and how did you find out?