I don't agree with that assessment, so yes, I will push it.
The Watching Ward is a far more versatile ritual than a regular ward, but let's not forget that despite its name, it's not a ward but a trap. They don't serve the same purposes. Wards are general defenses that keep things protected from the corresponding Form, while a Watching Ward is intended to go kablooey on the first threat that meets the triggering conditions. Even without discussing wards with additional effects, I'd believe that magi in Mythic Europe don't favor wards over the Watching Ward nor vice versa simply because they serve different purposes, not because their comparative usefulness. But let's also cover the specifics.
First of all, the Watching Ward only needs to be as powerful as the combined level of the spells it contains. Adding effects to a regular ward requires to increase the spell's level depending on how many and how powerful they are, because it's a single spell. This affects Penetration, and can lead to spells powerful enough to cause warping and even to reach Ritual requirement.
Second, while you can specify very particular conditions to trigger a Watching Ward, regular wards only act on contact, don't discriminate targets and can only affect the corresponding Form. To overcome some of these differences you'd require more effects, such as an Intellego requisite to identify particular foes, plus any additional Form that you wish to affect. Each of these requisites increases the spell's level as well, and it'd still be limited to affect things by contact, which I'm not sure how could be expanded (Although there's that spell you mentioned many posts earlier which triggers by looking at the target, so it could be conceived). If allowed, doing so would further increase the spell's level anyways (in that example, it corresponded to extending the target to T: Room, but the target still was an individual, so I'd consider that you would add the cost for both targets/ranges).
Third, dismantling the Watching Ward, even if easily detected, is inherently risky, whereas nullifying a ward isn't by default, and it's even easier if it's a circular ward. It'd be also easier to locate such wards due to their level, and this would also increase the difficulty when trying to shroud them.
So, to emulate a Watching Ward as a permanent trap, you'd effectively need to design at least three effects into a single spell, which according to the rules for Requisites would add two magnitudes to the base effect. Depending on how powerful the additional effects are, they might cost extra magnitudes. Including other Form requisites so you can affect them would also cost extra. Triggering the ward by other means than by touch would cost extra if allowed. And since it's a ward, that's just what you need to affect things with zero magic defenses, so feel free to add as many levels as you intend to penetrate. I didn't do the math on any specific example, but I doubt you can design such a ward to be useful without either reaching Ritual level, nor making it too weak or stupidly specific to be a threat to any decent magus, and even then, it can be safely removed when found.
For T: Individual wards, you're correct in that they can work both ways, allowing them to be used offensively. But you deliberately forgot that unless designed with a prohibitive number of requisites, they wouldn't tell friend from foe. An army warded with individual anti-personal spells would result in catastrophic consequences, and any ward against any kind of weapon would affect their own as well. Overcoming those inconveniences would raise the spells' powers above warping level, surely, if not Ritual as well.
So, nope, I don't think that magi in Mythic Europe would stop using Watching Ward spells to favor modified wards, any more than they would do with regular wards, anyways. Modified wards would be extremely useful for very specific purposes, but also extremely costly, hazardous and vulnerable for reliable permanent defenses. One thing is to ward your camp with a circle that kills predators, and a whole different thing is to fortify your sanctum.
[Edit]: to summarize.