I tend to agree with you. A full synthetic 5W30 will serve most people very well most of the time, barring the extreme conditions.I've always believed that 5w30 is the best compromise between mpg and a long lasting engine. Kind of right in the middle of old school thick and modern too thin for my taste.
If you want to fine tune it, you can get a thicker 5W30 A3/B4 oil for European vehicles or more performance applications, or a thinner 5W30 Dexos1-Gen2 / GF-6 oil for more fuel economy and commuter applications.
Right now I’m running Edge 5W30 in one car and Magnatec 5W30 in the other.