This is what Apple claims and I don’t think you should believe it at face value. The EU has an entire team working on negotiating the boundaries with gatekeepers. They have a vested interested in compliance. Apple’s claims don’t sound credible.
The DMA requires interoperability so it requires being able to swap out Siri - completely. Competitors would need to be first class components with full system access. Apple has a long history of anti-competitive action in iOS. For example, Apple doesn’t allow full system cloud backup competition. One must use iCloud or it’s impossible to back up an iPhone over the air.
I side with competition and choice. If people want to use something other than iCloud, or Siri, they should be allowed to do that with their own hardware.