“Disbelievers” are referenced numerous times in the Qur’an, agreed. This mention of “disbelievers” is far more frequent than the nuanced concept of apostasy from Islam.
Freedom of belief can be (1) freedom to join (2) freedom to leave. Not all concepts are explicit in all references (I’m not suggesting they need be either, to be sure).
Qur’an 4:137 on belief and disbelief in alternating states, as well as Qur’an 2:256 that you mentioned earlier, about no compulsion in religion are indeed, on the surface to me, good points in favor of the Qur’an allowing apostasy without earthly reprisal — presuming no abrogation theory is embraced.
You’re right to say that denying abrogation makes a stronger case for a more peaceful rendering of the Qur’anic message.
Having only skimmed the arguments on the pro-abrogation side, and the sheer volume of theologians it has had on side for centuries, I do believe we cannot discount that view as “not Islam”.
Even those who don’t employ abrogation, will reference concepts like 4:137 as being bound to a 3-day period of allowing one to recant their apostasy. That doesn’t technically contradict the Qur’an. It can work alongside 4:137. It can also work alongside 2:256 for those who interpret the latter as meaning there’s no compulsion in accepting Islam.
I know, it sounds silly to me too — but such interpretations have been around for centuries and not trivial in their following and impact.
Finally, I’ve talked to Salafi Muslims who say that rejecting Islam — even atheism — isn’t punishable by death because of 2:256. However, “preaching” atheism or critiquing Islam falls under the “creating disorder in the land” verse (Qur’an 5:33), which does carry the punishment of death — whether crucifixion or the cutting off of hands and feet on alternate sides.
I find the author of the Qur’an not very kind to humanity, given their use of the ambiguous, open-ended phrase about “creating disorder” in Qur’an 5:33.
So back to vocal ex-Muslims who reject bigotry but make no apology critiquing the ideology of Islam and inviting others to reflect on their own Islamic beliefs; we have legitimate concerns from what has been the majority view across both time and population of Islamic civilization, in these matters.