In some ways, that arrangement seems like the worst of both worlds.
Unless everyone in the org works the same three days a week in-office, now you've got some people in office, some people still working from home, and coordination becomes more complex.
Have you ever been on a Zoom call where half the people are in a conference room and the other half are working from home and calling in individually? It's a mess. Either the in-office workers completely dominate the conversation, or, if it's more evenly matched, it's a lot harder to understand the in-office people unless you have really carefully calibrated microphones for the room.
Even if they were to agree on T/W/Th as everyone's in-office days, and everyone works from home on M/F, now you've got a large office space that is practically vacant for more than half of each week.