A recipe that specifies whole cumin and one that specifies ground cumin are asking for different things at different moments. The difference is about release rate rather than quantity.
The flavour is held inside oil cells
Most of a spice's aroma comes from volatile oils stored in small structures within the seed, bark or pod, protected from air by the surrounding material.
An intact spice therefore holds its aroma almost indefinitely, which is why whole spices bought a year ago can still smell strong when crushed between the fingers.
Grinding ruptures those structures and exposes everything at once, so ground spice begins losing aroma from the moment it is milled and continues losing it on the shelf.
Whole spices need fat and time
Because the oils are enclosed, heat has to penetrate the whole spice before anything is released, which takes longer than most cooks expect.
Hot fat is the efficient way to do this, since oil conducts heat well and then dissolves the aromatic compounds as they emerge, carrying them into the dish.
This is the mechanism behind starting a dish with whole spices in hot fat, and it is also why the same spices dropped into a simmering liquid contribute far less.
Ground spices release immediately and burn quickly
With no protective structure left, ground spice gives up its aroma within seconds of meeting hot fat, and shortly afterwards begins to scorch.
Scorched ground spice turns bitter and cannot be corrected, which is why ground powders are usually added after the onions and often with a splash of liquid to hold the temperature down.
The narrow window between fragrant and burnt is the practical reason recipes are so insistent about the order in which spices go in.
Roasting before grinding changes the flavour again
Dry roasting a whole spice drives off moisture and triggers browning reactions among its own sugars and proteins, producing compounds that were not there before.
The result is deeper and nuttier but less bright, since some of the delicate volatile compounds are lost to the air during roasting.
A blend made from roasted spices and one made from raw spices of the same composition are therefore different products, not variations in technique.
Grinding fresh is a timing decision
Spice ground at home is stronger than the same spice bought ground, so quantities from a recipe written for shop powder will be excessive.
Commercial grinding also generates heat, which drives off some volatiles before the powder ever reaches a jar, and the jar then loses more with every opening.
Keeping spices whole and grinding in small amounts is less about authenticity than about controlling when the clock on that aroma starts running.