The following on SOAP API seems to be possible, but in REST API with say 50 activity types on the system I would have to make min 5 REST calls. Is this correct or is there a better way?
"getLeadActivity" allowed you to return all activity for a lead without providing activity ids or calling many times. getLeadActivity » Marketo Developers
" If you want all activity types, a blank value needs to be passed."
"Get Lead Activities" Get Lead Activities » Marketo Developers
Comma-separated list of activity ids, max 10. Obtain activity ids by calling Get Activity Types.