The closest thing we had was the System Shock duology, since both predate Deus Ex. Deus Ex was basically accessible System Shock. Having dialogue trees and NPCs without losing the open-ended nature of System Shock’s more dungeon crawl-y approach was the real selling point.
You’re clearly misremembering System Shock if that’s what you think. Those games were just Ultima Underground with guns, especially the first. Deus Ex was soooo beyond dungeon crawler, it was almost a full blown RPG by modern standards, it had big hubs with multiple NPCs that you could talk, quests with alternate endings that sometimes changed later sections of the game, highly interactive environments, level design with lots of verticality and hidden paths… System Shock had nothing of that.
Really, if anything Deus Ex owes more to Thief in the gameplay department than System Shock, the interactive environments and very detailed level design, even the stealth were straight out of Thief. It clearly has some inspiration from System Shock, especially with the augments, but even those were more useful in ways to allow you traverse the environment than the former. Calling it an “accessible System Shock” is reductive at best.