Alister McGrath on Understated Tritheism in the Cappadocians

The notable writer Alister McGrath (a Trinitarian himself) writes concerning the Cappadocian notion of God in three persons:

"We are asked to imagine three human beings. Each of
them is distinct; yet share a common humanity. So it
is with the trinity: There are three distinct persons,
yet with a common divine nature. When all is said and
done, this analogy leads directly to understated
tritheism. Yet the treatise in which Gregory of Nyssa
develops this analogy is entitled That There Are Not
Three Gods! In fact, Gregory develops his analogy with
a degree of sophistication which blunts the prima
facie charge of tritheism; however, even the most
studious reader of the work is often left with the
lingering impression of three distinct independent
entities within the trinity" (Christian Theology: An
Introduction, page 302).