These particular restrictions make no sense.
1. Warnings should be allowed by anybody against anybody. They should lower relations, and they should not block a return warning. The only reason people used to warn Ottomans as BYZ was to avoid being warned. It's stupid that a warned nation can't warn the other back though; I've never seen a strong gameplay justification for that, and yet it's the sole reason warning was taken from minor nations against majors. If you simply allowed them to be mutual, warning a major as a minor would have no upside and potentially a cost.
2. Guarantees are similar. Sometimes, a minor can throw a guarantee on someone that allows said minor to alter the outcome of the war. I've done this as Kochin in the Vijay/Bahmanis war in the past; an extra 5 units joining a battle at the right time between two nations with 11-14 fighting each other can be decisive, but now that's gone because...why exactly? The only gameplay reason that comes to mind is people using guarantees for the relations, but you could just as easily have relations scale on relative power so that majors don't take guarantees from minors seriously on the relations front, while minors appreciate the help.
In both cases, we're getting reduced player agency where it's hard to see the gameplay reasoning, with minimal historical reasoning.