The work focuses on the strength and ductility performance of UHPFRC-RC composite structures, promoting UHPFRC as a protective/reinforcing layer for new construction. Design standard SIA 2052:2016 boosted UHPFRC applications in Switzerland. Data analysis shows that the national technical community regards UHPFRC mainly as a material to enhance the resistance and durability of existing structures. While the increase in strength provided by UHPFRC is evident, assessing deformation capacity for new or repaired structures is critical. Moreover, the ductility of structural elements is pivotal in various approaches, from seismic design to traditional plasticity theory methods for moment redistribution, from warning before failure by large deflections to resistance against imposed deformation. To fully exploit UHPFRC as a valid alternative to traditional materials for new construction, research must focus on this critical aspect at an experimental and numerical level to provide engineers with sound structural design tools for safety checks and assessment. The paper showcases M-N interaction domains and moment-curvature curves for different structural and sectional configurations and critically compares numerical and experimental results. Additionally, it demonstrates how traditional numerical methods for the non-linear analysis of RC structures fit the assessment of (R)UHPFRC-RC composite structures. UHPFRC jacketing of traditional RC structures is a promising solution to retain adequate strength and deformation capacity while preventing aggressive deterioration mechanisms. Finally, the work lays the foundation for further reflections on the actual deformation capacity of structural members repaired with UHPFRC, addressing some common criticisms and ensuring the widespread application of a sustainable and durable material.