Not true, and v.8 establishes the context that tells us there is nothing that is not subjected to Christ. And, all subjected to Christ will be saved.
"many sons": the verse says "in bringing MANY SONS unto glory"; that is, only those who are God's "sons" - those whom He had chosen to adoption, become saved. Not everyone is a son, or a child of God - it was God's divine prerogative to choose whosoever He wanted to, as sons/children to adopt them, leaving out those whom He would not choose to adopt as sons/children.
For example, look at it this way: a king can bequeath his kingdom unto his son, making him king to reign in his stead, putting everyone under his subjection, but that doesn't mean everyone put under his subjection automatically becomes sons/children too. Nor does it mean that the new king is compelled to treat non-sons as sons. As king, he has the authority to place sons/children under one law, but to keep non-sons/non-children under different law - such is the power of a true king.
Observe "SONS" in the following verse. that it is only the sons who are brought unto glory, not everyone.
[Heb 2:10 KJV] 10 For it became him, for whom [are] all things, and by whom [are] all things, in bringing
many sons unto glory, to make the captain of their salvation perfect through sufferings.
By the "us" (below) we are informed that the adoption is only to certain specific people, but to not everyone.
[Eph 1:5 KJV]
5 Having predestinated
us unto
the adoption of children by Jesus Christ to himself, according to the good pleasure of his will,
Who are the "us"? Those whom God chose before the foundation of the world:
[Eph 1:4-5 KJV]
4 According as he hath chosen
us in him
before the foundation of the world, that
we should be holy and without blame before him in love:
5 Having
predestinated us unto the adoption of children by Jesus Christ to himself,
according to the good pleasure of his will,
If not already obvious, based upon the following verses, we can know that the "us" and "we"(etc) do not include everyone. Observe in them, the "death unto death" and the "life unto life". They mean for the unsaved, that physical death is unto spiritual death, but for the saved, physical life unto spiritual life.
[2Co 2:15-16 KJV]
15 For we are unto God a sweet savour of Christ,
in them that are saved, and in them that perish:
16 To the one [we are] the savour of
death unto death; and to the other the savour of
life unto life. And who [is] sufficient for these things?