This is not technically correct. If you configure a Powerwall system with too much solar it won't self-destruct or "fry something". It will simply not work well. When the solar ramps up and the Powerwall gets full or approaches the maximum charging rate when off-grid, it will raise the frequency to try to curtail the solar. Most solar inverters don't do good proportional curtailment, so it will simply shut down. This means that the Powerwall could be empty and need charging, but the solar is too powerful and the Powerwalls won't charge. This is why it is treated as a design rule.
I have solar based on Enphase micro-inverters. I have one old system (M215) and one new system (IQ8). On both of these systems, it's possible to simply shut down sections of the solar by turning off breakers in 20A increments. So, I would not hesitate to put all the solar on the backup side of the system because I could just turn off portions of the system to remain below the maximum Powerwall charge rate. When you are in a grid-down situation, it's best to have all the solar available.
I should mention that if you have variable loads available like a Tesla car to charge, you can keep all the solar running full blast and vary the car charging to absorb the surplus solar that the Powerwall can't accept. However, this is an interactive solution just like turning off part of the solar. As I recall, the OP mentioned that this is like a vacation home, so he should really see if he can divide the solar so a portion is on the non-backup side of the Gateway so that the whole system can run fully autonomously without overloading the Powerwall.