In the absence of a true 3 down ILB, equally effective in both run and pass, you're looking at 3 players.
Lets say your 3 down guy's strength is in coverage, a WILL (derived from "weak side") type, which is kind of misnomer since he may often line up over the TE in a coverage role or in various front alignments. Positioning is a matter of matchups, game plan, down and distance. Anyway, that's the Littleton or Queen type.
So, first you have base downs, 1st. down against half or most opponents, short yardage, goal line, and maybe more against opponents that like to run a lot. In that case, you need that run stopper on the field. That's your Goodson-type or Ragland-type in my hypothetical Queen-Ragland combo. That's accounts for 30% of snaps, give or take from week to week depending on matchups and how down-and-distances happen to fall out.
At the other extreme, there are the obvious passing downs where you would swap out that Goodson-Ragland type for that hypbrid ILB. Going back to an an earler discussion, whether you call that guy an ILB or a box safety or a DB, and whether you call that a nickel or dime defense, is a matter of positioning in my mind. If that guy is in the box in a ILB position, to play press over the TE or blitzing or dropping in short zone, he's an ILB in a nickel coverage. If he's outside the box he's a DB in a dime coverage or quarters coverage in a rush-3 call.
Regardless of what you call that guy or what you call that defense, Goodson or Ragland is not the optimal guy for a coverage or blitz assignment. So, in comes your hybrid strong safety type, variously Greene or Ibrahim or Amos very briefly early last season or some
Then there are the mass of tweener downs, anything from 2nd. and 8 to 3rd. and 2 depending on that offense's habits, field position, game situation. For example, whether McCarthy or LaFluer, you could probably count the 3rd. and 3 runs over the course of a season on one hand, maybe one finger. So the rotational down split between your run stopping specialist base player and your hybrid ILB player would vary from game to game according to the game plan or injury/availability.
Rotational specialists are not expensive even if they are good enough to fill their role. You don't want a guy who is a stiff in the other aspects of the game for those snaps where the offense crosses you up. That's why hybrid ILBs are strong safety types and not CB types who have some chance of making a play in the run game and you don't want some leadfoot in the base D who can't do something if the play is not a run between the tackles.