CathInfo.com

Yes, we can all speculate - e.g, your "it's likely . . . " For example, St. Robert Bellarmine was of the opinion that St. Augustine did not hold that the infants were burned.

That is why I want to consider what he actually said and thought, as he himself expressed it.

Neither of these theologians [Bellarmine or a guy named Petavius], however, succeeded in winning a large following or in turning the current of Catholic opinion from the channel into which St. Thomas had directed it. Besides Natalis Alexander (De peccat. et virtut, I, i, 12), and Estius (In Sent., II, xxxv, 7), Bellarmine's chief supporter was Bossuet, who vainly tried to induce Innocent XII to condemn certain propositions which he extracted from a posthumous work of Cardinal Sfrondati and in which the lenient scholastic view is affirmed. Only professed Augustinians like Noris and Berti, or out-and-out Jansenists like the Bishop of Pistoia, whose famous diocesan synod furnished eighty-five propositions for condemnation by Pius VI (1794), supported the harsh teaching of Petavius. The twenty-sixth of these propositions repudiated "as a Pelagian fable the existence of the place (usually called the children's limbo) in which the souls of those dying in original sin are punished by the pain of loss without any pain of fire"; and this, taken to mean that by denying the pain of fire one thereby necessarily postulates a middle place or state, involving neither guilt nor penalty, between the Kingdom of God and eternal damnation, is condemned by the pope as being "false and rash and as slander of the Catholic schools" (Denz. 526).

This condemnation was practically the death-knell of extreme Augustinianism, while the mitigate Augustinianism of Bellarmine and Bossuet had already been rejected by the bulk of Catholic theologians. Suarez, for example, ignoring Bellarmine's protest, continued to teach what Catharinus had taught — that unbaptized children will not only enjoy perfect natural happiness, but that they will rise with immortal bodies at the last day and have the renovated earth for their happy abode (De vit. et penat., ix, sect. vi, n. 4); and, without insisting on such details, the great majority of Catholic theologians have continued to maintain the general doctrine that the children's limbo is a state of perfect natural happiness, just the same as it would have been if God had not established the present supernatural order. It is true, on the other hand, that some Catholic theologians have stood out for some kind of compromise with Augustinianism, on the ground that nature itself was wounded and weakened, or, at least that certain natural rights (including the right to perfect felicity) were lost in consequence of the Fall. But these have granted for the most part that the children's limbo implies exemption, not only from the pain of sense, but from any positive spiritual anguish for the loss of the beatific vision; and not a few have been willing to admit a certain degree of natural happiness in limbo. What has been chiefly in dispute is whether this happiness is as perfect and complete as it would have been in the hypothetical state of pure nature, and this is what the majority of Catholic theologians have affirmed.

Then it continues:
So, for the past several hundred years now, there are practically no theologians who have held that unbaptized infants go to Hell and suffer anything at all.  Why is it OK for individuals to reject this, including the same ones who keep arguing the "450 years" in support of BoD?

I hold the same opinion that was described that Suarez held above.

But, despite several hundred years of near-unanimous theological opinion in favor of Limbus Infantium, I do not claim that someone is condemned as a heretic for rejecting that Limbo, since it's not been actively taught by the Magisterium nor has the opinion of St. Augustine been condemned.  I'm consistent there.