The wpdb logic is an addon and only triggers if wpdb is found. Phptop might still be useful in the general case to quickly and cheaply find CPU hotspots.

Nowadays it would be necessary to also show the various Curl/API calls because they're so omnipresent and impactfull on PHP sites (as wait time and not CPU time)... But AFAIK it's pretty hard to intercept them in a generic way.