Your market can heavily impact how easy it is to find a property with decent cash flow, so it's possible you just live in a good environment.
That said, there is a very serious trap that you can fall into by following these rules of thumb. Cheap (read D-F class) properties fulfill the 1-2% rule very easily. However, If you invest in these very cheap D-F properties, reality often underperforms the paper proforma returns for a couple of reasons:
1) Tenant class is lower, leading to higher turnover costs, increased risk (especially in COVID) of non-payment issues
2) Capex costs. For some reason, all calculators take capex costs as a % of rent. This is stupid. Capex is determined by the cost of a large capitalizable item divided by its useful life. A roof or a water heater costs about the same to replace for a small house as it does for a larger house, meaning that its cost is a higher percentage of rent than a larger house would be (and a higher percentage than what most online calculators will say).
This isn't to say that you can't make these work or even that the houses you're looking at are like this, but it's just something to consider when analyzing your properties.