There’s no need to retreat to a hermitage (though I agree it has its appeal at times) for an ‘I don’t like my new vape’ problem. Such problems are very common, but almost always solvable. Sometimes the solution involves buying more kit, but with the combined wisdom of ECF brought to bear on the issue we should be able to help you minimize expenditures.
@Superuser187 has the temperature issue covered. People prefer different temperatures. Some pod mods cater to this by offering different coils and/or different settings so you can adjust the temperature, but the Caliburn A2 doesn’t seem to be one of them. If the temperature is a deal-breaker, you might want to try an adjustable mod.
About the juice, it may be as simple as needing a different brand. Flavours vary a lot from brand to brand – both the flavour itself and the sweetness. Someone else’s watermelon might be milder and less sweet, suiting you much better. The best way to find out is trial and error. Most of us have countless bottles of juice that didn’t work out.
Onto nicotine. Your conversion is correct – 5% is the same as 50 mg/ml. However, I believe there are different ways to make salt nic, so different manufacturers’ salt nics can feel a little different even when they’re the same strength. Again, a different brand of juice might work better for you. It’s also possible that the warmer (and probably thicker) vape is affecting the throat hit and the way you’re perceiving the nicotine, so a pod with a cooler vape might help.
Good luck, and keep asking questions!