They are not a spotter and a screen. They are a 1 DP splash and a 3 DP whole army, aimed at different collections.
[Abhuman Auxiliaries](/40k/armies/astra-militarum/detachments/abhuman-auxiliaries) (1 DP, Take and Hold) is a specialist bolt-on. Its rule covers three datasheets, it has three stratagems and two enhancements, and both enhancements are 10-point Upgrades on units rather than character relics: Exemplar of Duty gives a Commissar Feel No Pain 4+, and Sharp Eyes, Light Fingers gives Ratlings a detection effect. It does nothing for your infantry, tanks or artillery, adds no damage of its own, and will not absorb command points. It is designed to leave 2 DP for a detachment that does something else entirely.
[Grizzled Company](/40k/armies/astra-militarum/detachments/grizzled-company) (3 DP, Priority Assets) is an army-wide Order engine. Ruthless Discipline adds 1 to the number of Orders each ASTRA MILITARUM OFFICER model can issue, and gives every unit affected by an Order a re-roll of Hit rolls of 1. Three of its four enhancements grant entirely new Orders, so the detachment compounds with itself. Its ideal list is many Officers and many squads, and Ogryns are a small part of it, reached through one 20-point enhancement.
So the two want different armies. One is a package for a player whose army is mostly not abhumans. The other is a package for a player whose army is mostly Officers and infantry, where Ogryns are a garnish.
The shared stratagem-level signal that Games Workshop wrote them as alternatives is the Abhuman Detail enhancement itself: it exists because Grizzled Company cannot take Abhuman Auxiliaries. It is Grizzled Company's built-in answer to the abhuman question, priced at 20 points instead of a Detachment Point.