It doesn't necessarily assist chains, it complements the strategy of deep chaining. It covers other bases WHILE you deep chain certain targets. You are correct in that it does not assist chains at all, basically proving my point. Spells and ops are meant to damage things like economy, sustainability and province stability. Deep chaining is meant to damage things like attacker potency and impact.
When you have no spells or ops that really do meaningful damage to attacker potency, you are left with the need to deep chain them to impact them significantly in war. That has been taken away with the new gains formula; all well and good, I actually like it after getting used to it. But now you have to resort to finding other ways to reduce attacker potency, nothing of which you can find in spells or ops.
Let's look at the core of an attacker's impact; their offense. As long as an attacker has generals and offense, they will never stop steadily impacting the war.
Now, what can you do to an attacker with spells and ops:
Fireballs? Attackers can still keep attacking and receive gold aid to stay afloat.
Tornadoes? Too expensive and attackers can still keep attacking and receive gold aid to stay afloat.
Meteors? Too expensive and easily mitigated by keeping your offense out and away from that damage, so attackers can still keep attacking.
Night Strikes? Most offenses are mostly elite driven, you're not damaging much offense with this and thus attackers can still keep attacking.
Arson? See Tornadoes reasoning.
Steal Warhorses? Keep your horses out and you never lose a single horse, plus this means you are still attacking.
Propaganda? Too expensive and rarely touches offense, as offense is always out, which btw means you are still attacking.
Most of these spells and ops, you know what they do? They soften provinces so that they can be CHAINED more easily.
What has just been removed from the game as a viable strategy to remove the impact of an attacker? CHAINING.
So I maintain my stance that you have not provided anything new with which to approach the loss of deep chaining.
You expect us to just Ambush all war to kill offense perhaps? Maybe squat on provinces for the moment their armies get home and hope you catch it? Be realistic, most players are not glued to this game nor will they ever be. You need to provide ways to damage offense, plain and simple.
Maybe an op or spell that takes a General out of commission for a few hours. Something that kills a bit of offense while it's out on attack. You've steered the game away from deep chaining, so now you need to design things that present themselves as viable alternatives to be used strategically in war.

