Not only that but I've found SPAs to be more complex than their traditional counterparts, mainly due factors like: the extra layers & complexity involved, churn

Not only that but I've found SPAs to be more complex than their traditional counterparts, mainly due factors like: the extra layers & complexity involved, churn rate of & lack of maturity in JavaScript frameworks, lack of integration with backend of choice. Of course there are advantages to SPAs and this generally is my choice of architecture, however I definitely wouldn't say that SPAs are more agile at all.