But if you go on isthereanydeal.com you will see a whole bunch of online stores that offer sales on games. They offer Steam codes too but are not limited to Steam, they cover many other platforms (including Epic).

(Those btw are all legit sites showing only sales endorsed by the game publishers themselves, they all sell new game codes. ITAD has a standing policy to only source from that kind of sales, strictly no key resale sites.)

So if you can get Steam games cheaper than are currently listed on Steam, and many games are also available on GOG which is DRM free... not entirely sure what this lawsuit is about.

I though that Steam required content parity e.g. you cannot create a cheaper bundle for your own storefront and not sell that exact bundle on Steam. But they have no issue with you generating keys on their platform and either sell those off for cheaper yourself (Humble bundle) or give them away.

They won't. They're here to blindly defend a multi billion dollar company despite it actively costing them more money.