This study investigates the dynamic stability of the Martinique island power system under a projected high-renewable worst-case operating scenario characterised by a major reduction in synchronous generation and a corresponding rise in converter-based renewable supply. In the considered operating condition, a total system demand of approximately 185 MW is largely supplied by photovoltaic and wind generation, while only about 19 MW of diesel-based synchronous generation remains online at the main generation site, compared with around 120 MW in a more conventional operating regime. The shift yields a low-inertia, converter-dominated grid, increasing vulnerability to disturbances and post-fault instability. The contribution is a consistent comparison of GFM BESS versus synchronous condensers under a common worst-case fault disturbance on key frequency stability indicators. The dynamic analysis simulation is carried out in DIgSILENT PowerFactory 2024 using RMS simulations. Two reinforcement strategies are assessed against a baseline case without additional support: Virtual Synchronous Machine (VSM)-based Grid-Forming Battery Energy Storage Systems (GFM BESS) and synchronous condensers. The GFM configuration includes two 24 MVA grid-forming converters installed at different substations, each operating with an inertia constant of H = 2 s. The synchronous condenser configuration consists of two parallel 23.5 MVA synchronous condensers with H = 3 s and IEEE AC1A excitation control. In order to test the system under extreme stress, a three-phase solid fault with zero fault resistance is applied on a close distribution line for 200 ms, followed by disconnection of the faulted section. The results show that both technologies improve post-fault dynamic performance relative to the baseline case, but through clearly different mechanisms. The GFM BESS configuration provides faster transient support and reduces the initial speed excursion of the remaining synchronous generator, with the peak speed deviation limited to about 1.020 p.u. compared with nearly 1.028 p.u. in the base case. It also enables faster voltage restoration. However, its performance is strongly affected by current saturation and electrical proximity to the fault. In particular, the GFM unit located closest to the disturbance reaches its 1.0 p.u. current limit almost instantaneously and exhibits control-induced oscillations during the recovery period. By contrast, the synchronous condensers deliver strong reactive power support, with reactive output increasing from about 28 Mvar pre-fault to a peak of approximately 73 Mvar during the event, resulting in smoother voltage recovery and better-damped electromechanical behaviour. In addition, RoCoF analysis performed using 100 ms, 250 ms, and 500 ms sliding windows reveals a time-scale-dependent trade-off. Although the GFM-based solution produces higher peak RoCoF values over short windows, it achieves better stabilisation over longer windows than the baseline case. The obtained results show that GFM BESS and synchronous condensers improve post‑fault stability through distinct mechanisms and are therefore complementary rather than interchangeable reinforcements in low‑inertia island grids. They also underline that converter current limits, asset location, and the selected dynamic performance metric must be explicitly considered when designing resilient low-inertia island grids with high renewable penetration.