Note that the 4MB number comes from a single network metric.
>Our results hinge on the key metric of effective throughput in the overlay
network, which we define here as which blocks propagate within an average
block interval period the percentage of nodes to.
...
>Note that as we consider only a subset of possible metrics (due to difficulty in accurately measuring others), our results on reparametrization may be viewed as upper bounds: additional metrics could reveal even stricter limits.
It says nothing about any mining centralization pressure, DoS attacks, etc. A single metric among many we have to contend with.