That could be a US/UK difference in terminology. In the US Doubletree is definitely full service. The problem with its positioning within the brand portfolio is that officially it offers the same features as a Hilton while in practicality it's often clear it's a poor cousin. That's also how I see CP relative to its supposed competition of Marriott and Hilton: the brand claims to tick all the same boxes but it practice it's a cut below.