OPM is the layer that makes good delivery systematic rather than heroic. Organisational enablers — a PMO, consistent & tailored methodology, governance, capability development, knowledge management — are what turn one good project into a repeatable capability.
Maturity = the ability to deliver consistently & predictably. The improvement cycle repeats:
Progression of practice: Standardise → Measure → Control → Continuously Improve (SMCI), built from best practices → capabilities → outcomes → KPIs.