Your points are valid.
Unfortunately, JWs have been conditioned to believe that, in order for WT doctrines to be true, they MUST change. This is called "progressive". Churches of Christendom are harshly condemned by WT for not changing most of their doctrines in hundreds of years. This is seen as a flaw in their theology.
This is why JWs get so excited whenever "new light" is presented- it's further 'proof' that the WT is God's Organization. If JW doctrines remained consistent and unchanged it would be viewed with suspicion and an indication God is not actively directing his "sole channel of communication on earth".
Of course, all of this ignores the simple fact that, if something is indeed true, then it does not, and cannot, change. Truth is truth.
Each "new light" change is touted as having solid scriptural basis and directed by Holy Spirit. When that current teaching expires, then the replacement doctrine is justified using the same distorted logic. What's worse, occasionally WT blames god for the error- he taught a lie in order to "test" Jehovah's Witnesses' faith. You see, in WT mentality, the god of truth requires you to believe lies- and if you have the audacity to reject lies, then god has no place for you in his organization. The WT worships such a nice god !