You're assumption is that all of these things need to occur as if to prove your point. What basis for each scenario are you using for your assumptions?
Basis for Cargo ship delays: Distance between ports is unknown, as map would be inaccurate as lines of latitude in southern hemisphere are much longer than expected, and landmasses are assumed to be the same size as is currently believed, thus at least one of the bodies of water is going to much larger than expected, and cargo ships crossing it will take much longer to cross it. Alternatively, the bodies of water are the same size as currently believed and at least one of the land masses is much larger than expected, and going around them, or land based cargo transport going across them will take much longer than expected.
Basis for Submarine cables: Again, problems with the size of the bodies of water or land. There's no way you can run cables from Spain down to the Caribbean, around the coast of North and South America, across to Hawaii, down to New Zealand, up to India, down to South Africa and back around to Europe without finding a problem somewhere.
Basis for GPS Problems: A GPS signal contains information on the time, and the position of the satellite in it's orbit. Having the satellites all orbiting in a ring above our heads along the equator has the problem that none of the satellites will be where they say they are, and thus the GPS receiver won't be able to calculate it's position accurately based on the time delay between the signals received. Much the same problem with having the GPS system ground based, with the added problem of the signal used rapidly attenuating in the Atmosphere.
Basis for gap filled maps of the seabed: The sea's a completely different size to what's expected. Unless the land masses are stretched out of proportion, where the problem with maps of the land being gap-filled comes up.
Basis for Weather problems: A weather front moving around in the southern hemisphere is going to have a completely unknown distance to move, so there's no way we could predict when it's going to turn up. Much the same problem with hurricanes.
I would think these things are fairly obvious. I shouldn't have to explain each one individually...
wouldn't say they can "easily be accurate" because if the Earth is round, projections are used for maps.
Not everyone uses a map of the whole planet with a Mercator projection. Just because projections exist doesn't mean people use them as a reliable global navigational aid.