Thought experiment: how many arcane spellcasters in a fantasy combined arms army

[Bucky]

It looks like I messed up some of the details. Do they undermine the point, though?

The hunter-killer team executes a mission with the following steps:

1. Locate a target
2. Get the whole squad in position to attack the target
3. Isolate the target
4. Kill the target
5. Get away

They do this on two scales, one on which the target is a group (like a patrol or an adventuring party) and one on which the target is a specific member of that group (like the patrol's courier or the party cleric), although at both scales the third and fifth steps might be carried out by killing enemies other than the target.

The non-casting members of the squad contribute...
...to the first, only at small scale,
...to the second, little beyond the liability of needing to position an extra person,
...to the third, mostly at the expense of the fourth by attacking targets other than the main one,
...to the fourth, as their main contribution they dedicate most of their build to, and
...to the fifth only to the extent that escape involves killing more targets, otherwise they are a liability.

If you have any suggestions for doing these mundanely, particularly at the large scale, I'd like to hear them. As spec'd now, though, the scouting is mostly done by divination and animal companions, the mobility uses mounts but needs magic to fill in for mounts' weaknesses, BFC spells are by far the best way to pick apart groups, and BFC spells and speed buffs are also the tools of choice for helping the mundane or slower members escape a bad situation, particularly since the enemy can kill the mounts.