Search for "Redump PS2 CHD" on the Internet Archive. These are legal archival dumps. While not "ultra compressed" by default, community members upload CHD packs that reduce 1 TB of PS2 games down to ~400 GB.
Highly compressed files are digital disc images reduced in size to save storage space while remaining playable on emulators or soft-modded hardware. While a standard PS2 ISO typically occupies about 4GB , advanced compression can shrink these files by 30% to 60% without losing original game quality. Popular Compression Formats ps2 iso files highly compressed full
For Steam Deck owners, Android retro gamers, or anyone with a medium-sized external drive, highly compressed PS2 ISOs are a game-changer. You can fit the entire top-100 PS2 library on a single 256 GB microSD card. Search for "Redump PS2 CHD" on the Internet Archive