Which is beautifully solved by armor and wound count
Disagree, unless you make the differences in wound count much more pronounced. Right now the difference is only significant when you compare individual models. The moment you compare it to a unit, even a MSU, behemoths are often not all that much sturdier anymore. And since we play with units, not individual models, this is the relevant comparison. And that's ignoring that the behemoth is also a hell of a lot more expensive than most MSU.
A msu of clanrats has more effective wounds than 1 Magmadroth (both unsupported). The cheapest magmadroth costs 230 points, 230 points worth of clanrat has about double the effective wounds. As a unit the magmadroth is significantly squishier, even though as an individual model he might be sturdier.
Doesnt at all address the clear problems with strength and toughness present in 40k.
As far as I know the "clear problems" are:
1) people find it confusing
and
2) 40K has managed to mess up the str and thoughness values to the point where a thoughness below X is worthless and above Y too good.
As far as adressing those go:
1) I find a non-issue. You're playing a wargame, doing the basic comparison that modern 40K uses should not confuse you.
As for 2) that's mostly a matter of establishing some basic design principles and not screwing that up. Not an inherent flaw to str v.s. thoughness systems. Personally I like the LOTR one where you never wound on better than a 3+, but weak attacks quite quickly lose power against strong defenses eventually just flat out becoming useless. This ensures anti-tank weapons are needed to deal with high armour, without making them crush any and all opposition instantly while at the same time a high volume of low strength attacks can be used as anti-horde weapons without them ever threatening tanks. Anyway, the tl;dr on this point is basicly just "don't screw it up"
Anything else you'd want adressed?
Both of these do not make any real distinction between the targets they fight and thus are useless to distinguish between different types of weapons.
Rend was clearly intended to give this distinction, but it falls flat since it gives the exact same relative increase; 1 point of rend always decreases the amount of succesfull saves by ~16% relative to not having that rend. Regardless of if you start with a save of 1+ or a save of 5+, you'l now be failing 16% more saves due to that 1 point of rend.
Abilities that give you reroll hits or more attacks when fighting large units.
This is better, but much like keywords ultimatly has limited uses before it gets confusing or messy. You got units of 20+ bodies of both hearthguard & clanrats. One of these is still supposed to be massivly better protected than the other. Yet your weapons is just as effective against either of them provided there's enough bodies to reach the cut-off point.
Is it because you want this kind of customization when building your list? I honestly dont feel the need for that at all. Lets say when I field 40 Skinks - I dont really care if the Boltspitters might technically be better against hordes with bad saves vs javelins that technically could be made stronger (with this S/T system) against Behemoths or high save targets. I really dont see the appeal to this and it isnt a problem I face. I dont play 40K but I can tell that people care ALOT about what weapon loadout they have on their tanks etc. I dont care about it.
I'd want it for 2 reasons;
1) I like it as it makes sense in my mind. It also allows for some customisation & personalisation which I like and currently miss.
2) I believe it'd significantly improve balance of weapons by allowing you to make weapons that are anti-tank, but that don't also wipe out hordes (and vice-versa). As mentioned before stuff like rend is just as effective at ripping apart clanrats as it is magmadroths. Similarly weak weapons with a high volume of power, like skinks with blowpipes, are just as dangerous to clanrats as to the magmadroths.
3) I believe it'd significantly improve balance of weapons by allowing you increase defenses without needing to increase their saves wounds or giving another ward save. A great example of this are the gargants. They need their 35 wounds otherwise they're simply going to be mowed down. But 35 wounds is so high that it ends up invalidating a lot of magic spells because the damage spells deal against single-entity units simply isn't very significant if that single entity has 35 wounds. A str/thoughness mechanic could've allowed the gargants to be fine with say 15-20 wounds, at which point magic starts doing reasonable damage again.
In my mind there is much more to the "toughness" of a dude than just his armor save. The amount of wounds is factored in and potentially ward saves.
To an extend yes, wounds are relevant. Essentially the important bit are effective wounds. However, this only really holds up in AoS when you compare models. A MSU of clanrats shouldn't be comparable in terms of effective wounds to a magmadroth. Now obviously you can make the magmadroth sturdier by giving him absurd saves, rerolls and wardsaves, but that creates other issues where these tanky units become unkilleable for certain factions.
The best way of explaining I can think of is to look at historical armour. A knight in full plate can basicly walk through a storm of arrows and not really care (unless he gets really unlucky). That same storm of arrows can kill hundreds of unarmoured peasants. It isn't until you bring out the extremely heavy warbows with specialised armour piecing arrows that the knight has to start worrying. Point being, anything capable of slaying that knight can slay hundreds of peasants.
And that's something you basicly don't see in AoS, something capable of slaying a heavily armoured chaos champion, or some giant behemoth can struggle to kill a unit of clanrats.
I think Stormcast is a bad example though because it has been an issue for a long time that they were considered super tanky but as AoS progressed onwards a 4+ save just isnt that great anymore. DoK and Fyreslayers are also examples of where warscrolls and the looks of the models just dont match.
AoS in general does not do a particularly good job at having the looks of units match their survivability, unfortunatly.
