This study compares reactive and capillary-driven (non-reactive) ultrafast sintering of simple versus compositionally complex silicides via different kinetic pathways. Four systems, VSi2, (Nb0.273V0.343Cr0.384)Si2, (Mo0.186V0.523Ti0.291)Si2, and (Mo0.081Nb0.197V0.25Cr0.3Ti0.172)Si2, were investigated. The compositionally complex silicides (CCS) were designed to achieve an average melting temperature comparable to that of VSi2 while maximizing configurational entropy under this constraint. For each CCS, capillary-driven ultrafast sintering was performed using pre-synthesized single-phase powders and compared with reactive ultrafast sintering starting from mixtures of three or five binary disilicides. Results indicate that reactive ultrafast sintering resulted in higher sinterability than capillary-driven ultrafast sintering, while increasing compositional complexity generally enhanced densification. Compared with capillary-driven sintering, the reactive process initially suppressed sintering but maintained high densification rates for longer duration, resulting in higher final relative densities. The grain size after ultrafast sintering was found to correlate with the final relative density, regardless of the composition or kinetic pathway.