You're missing the point. Yes, understanding the different layers involved in a network is important. But the OSI model is the wrong way to explain those layers, because it's a different network/software architecture from the one which was implemented in the Internet. The "blurriness" you're referring to in layers 4-7 is literally because those layers are describing software which was never written.
Oh, absolutely agree on that, trying to actually make the OSI model as it was intended a real thing in real life would be an utter exercise in futility. I was thinking purely of how the OSI model concepts can be mapped to things we have built and use now on LANs and WANs, as an educational/mental model concept.
