The contrary argument is reasonably well-stated within the article, it seems to be mostly a matter of what you assess to be the greatest risks going forward as to which argument you think is more valid.
After glancing at the endnotes, it seems that the bulk of the scientific references examining natural immunity date from before the delta variant established itself.
The reasoned answer is politics. One side of the aisle committed to a message before they had all the data. The other side did this too. Now it's too politically costly to change any of those positions, no matter how much anyone claims to "follow the science".
