No. I don't actually know how close they can be, but I'd say it's very rare for any two (different) monitors/speakers to sound the same in a blind listening test... I've never personally heard two speakers that sounded the same and I've never heard of different speakers that sound the same.... Maybe.... But I've never heard of it.
But with good monitors (and a good acoustic space) there shouldn't be any major defects or deficiencies. And monitor with an 8-inch woofer would need a subwoofer to go-along with it in order to get deep, strong, accurate, "realistic" bass...
If a mixing or mastering engineer is working in a new or unknown studio they will have to learn the monitors (and the room) and learn how to make good mixes on them. But they usually have a known-good reference track (or two) so they can adapt to the differences. And most pros will check their mix on multiple ("less perfect") setups before releasing their production, so they are not just relying on the studio monitors.
And they might decline an "upgrade" because it would learning the new monitors.