Muffled
Jesus in me
i hate to say it, but that verse doesnt say the ones clothed in white robes are in heaven. It says they are "standing before the throne and before the Lamb" but it doesnt say they are in heaven.
Chapter 19 only says John heard a multitude in heaven singing praise to God, it doesnt say these are 'the people from tribes and nation and tongues'
I agree. There is no designation of the place the throne. The realistic expectation is that it is in The New Jerusalem which is in the clouds.
The 144,000 are also not in Heaven but there is a later passage Rev 12, that suggests they are raptured early as a first fruit.