I see both sides of the argument but where Hullmod+ can really shine is do some fairly creative/off-the-wall things that "more OP" can't. More OP can give you more guns, more vents, etc. (which is all very good and straightforward) but what Automated Repair Unit giving 1% Hull Health/sec, what's that worth in OP (using the mod idea)? Boosts in speed, shield efficiency, less recoil, etc. are all difficult to quantify from an OP-perspective. The rub I could have is that you start taking hullmods exclusively for the bonus effect. As long as the bonus effect is more of a double-down on the primary effect, I'm good with it but I'd hate to see Improved Turret Gyros also give +15 top speed or some weirdness. It would be like min-maxing synergies for a Diablo character by putting points into skills you'll never use.
The other consideration is, assuming S-modded hullmods are permanent and no longer free, the "permanence factor" will weigh into S-mod choice. After all, it prevents you from swapping out builds willy-nilly and can narrowly define how the ship functions. Heavy Armor, for example, if it is still one of the most expensive hullmods, almost needs more reason to make permanent than a cheaper hullmod that the ship can "afford" more readily. Even ITU (which is almost universally useful), might need a little bit of a "sell" because if you ever decide to use SO with that ship, ITU is basically dead-weight. You sort of do that now but freeing up OP is a bit more forgiving then being stuck with extra armor that makes you less maneuverable.