If a FetchNode has no filter, then its estimate is equal to it's child estimate. In this case we can avoid estimating the child in this code block:

if (node->children[0]->getType() == STAGE_IXSCAN &&
static_cast<const IndexScanNode*>(node->children[0].get())->filter ==
nullptr && // TODO SERVER-98577: Remove this restriction
_rankerMode == QueryPlanRankerModeEnum::kSamplingCE) {

Thanks milena.ivanova@mongodb.com for discovering the redundancy.

This makes me think that we need cardinality and cost estimation counters which we could assert on that a certain query took no more than that many estimations.