"or simple derailler one cog on front, 7 on back"
Lot to be said for it - that's the configuration on one of my most used bikes.
But it's becoming more difficult due to 'fashion creep'.
I remember when six cogs was 'wow'. You could go into shops and 'build your own' with a complete range of cogs hanging on the wall (behind the counter). My choice was 14, 16, 18, 21, 24, 30 - SunTour.
Until then bikes were single speed, 3 speed (Sturmey), 5 speed (14-24 was a 'big' range) or ten with (usually) an amazing 52/49 double chainring set up.
A few years ago it was easy to get 11-34T freewheels and cassettes giving a range of gears that would suit most people with a single chainring (apart from serious off-road use).
Now it's just about 14-34T only - in 7 speed.
8,9,10 etc. give spurious extra choice with thinner components that are likely to wear out faster unless of high (expensive) quality.