As far as difference between chainrings. I run triples with 10 or 12 tooth differences between the big/middle rings

14-16 between the mid and small ones. redundant ratios are in edges of chain line displacement one doesn't use.

bigger mid-low gives new ratios on the low side 3 or 4 good, less hardly makes the granny gear worthwhile.

larger differences like using a TA cyclotourist cranks . big differences can be made, small mm bolt circle down to a fitting a 26t..

traveled with a fellow , his double was a 50 -28, most riding on the big ring, the 28 for climbing steeper slopes.
up shift on the crest of hills, makes the big upshift when the load on the chain is least.

not an uncommon practice on Classic French bikes in the 40's and 50's..


Leaving derailleurs aside, the 2 speed planetary Crank offers a 250% difference,
as if a 50 and 20 tooth gear combination.

My Brompton has a AW3 Sturmey Hub 15t cog, 54 tooth chainring , second low range as if a 21.6t gear
chain never moves off the cogs, 6 ratios are largely in 30~40% differences, with no overlaps.
lowest in high range to highest in low range slightly bigger, but no big notice

Rohloff engineered a similar set with a range shift, [7 speed x2] but engineered the gaps between ratios
to be within fractions of a percent of being 13.x % of each other from top to lowest.


One thing to bear in mind is OEM build ups are as much about price as specifications..

for buying a pallet of cases of a component from shimano will be a standard gear set.
Shimano engineers a fixed set to work together , so OEMs can expect after a quick installation they will work.

Customer can pick and choose at point of sale with dealer, for different than came out of the box ,
cost to be negotiated with dealer at that time...