Trustlessness is a binary option, not a spectrum. There is no such thing as 'more trust' or 'less trust'. It's either trustless or not, and Ark falls into the 'trustless' category.
Decentralization, on the other hand, is a spectrum, yes.
Decentralized ≠ Trustless.
Protocols/services can be:
  1. Centralized and trustless (LSPs & ASPs).
  2. Centralized and trusted (WoS).
  3. Decentralized and trustless (Bitcoin).
  4. Decentralized and trusted (Fedimint).