Yeah exactly.
Their "loss" is their failure to protect the holyland. You can also say they "lost" when Kizaru failed to capture the Strawhats or when the truth about Dressrosa was exposed, so on and so forth.
It makes sense when you factor in what they did immediately after. Like
@rerere posted before, they sent their CP-0 agent to stop Morgans from publishing the news, which does not make sense on the surface level since Morgans was going to publish about Sabo assassinating Cobra anyway. But it also highlights the Marines failure to protect the Holyland and to allow such an assassination to happen, which is exactly why they tried to stop/alter the narrative by threatening Morgans.
If you aren't biased by agendas, I think it's obvious that the "loss" of the Marines is their failure to protect the Holyland and not the individual Admirals losing.