This study reports the successful synthesis of a two-dimensional (2D) MoS2-Mo1-xWxS2 polycrystalline lateral heterostructure under precisely controlled non-equilibrium growth conditions using chemical vapor deposition (CVD). By modulating the growth temperature and carrier gas flow rate, a transition region within the heterostructure was induced, demonstrating an innovative approach to tailoring heterostructures through controlled growth conditions. Detailed characterization through optical imaging, Raman spectroscopy, and photoluminescence (PL) spectroscopy revealed the presence of polycrystalline domains and provided insights into the local crystallographic structure and composition of the alloy. The inner MoS2 domain exhibits a PL peak at 1.83 eV, the transition region Mo0.43W0.57S2 domain at 1.86 eV, and the outer Mo0.33W0.67S2 domain at 1.87 eV. Our results highlight the significant influence of growth conditions on the nucleation dynamics and microstructural outcomes of 2D transition metal dichalcogenide (TMD) alloys. The complexity of polycrystalline 2D TMD alloy formation and the interplay between nucleation site density, growth kinetics, and resulting microstructure are discussed. The Raman spectra and PL data provide valuable information on the composition and optical properties of the heterostructure. The Modified Random-element-isodisplacement (MREI) model was effectively used to determine the tungsten (W) element composition in different regions. These findings contribute to a deeper understanding of the growth mechanisms and alloying effects in 2D TMDs and emphasize the importance of precise control over growth conditions to tailor the microstructure for advanced technological applications. The ability to engineer such heterostructures with controlled properties opens up new possibilities for their use in semiconductor devices, optoelectronics, and other fields.