That is really sketchy advice. IANAL either, but since no part of 5E is covered by the OGL, if you are accused of infringing on 5E your adherence to the 3E/3.5 license is pretty irrelevant. Trying to use the 3.0/3.5 OGL as a smoke-screen seems like a pretty flimsy defense: it is certainly possible to produce a work that is derivative of both 3.0 and 5E and that's what WotC's lawyers would demonstrate, if it ever came to that. And it would be very easy for them to demonstrate that. Most judges are not stupid and really hate rules-lawyering. ;}
The companies producing material for 5E right now are doing so not because they have a strong legal case, but because they have balls. Even with a strong legal case, legal fees could drive a small company bankrupt really fast, while not even registering a blip on Hasbro's bottom line. That's a risk you take using someone else's IP without explicit permission to do so.
The companies producing material for 5E right now are doing so not because they have a strong legal case, but because they have balls. Even with a strong legal case, legal fees could drive a small company bankrupt really fast, while not even registering a blip on Hasbro's bottom line. That's a risk you take using someone else's IP without explicit permission to do so.