Laser beam welding of Al-Si coated 22MnB5 steel is challenging due to Al enrichment from the Al-Si coating, which promotes α-ferrite and Fe(Al,Si) intermetallic (IMC) formation, degrading joint performance. This study examines the effect of static-in-source fibre and dynamic beam shaping using a coherent beam combining (CBC) laser system during overlap welding, comparing core-only, static core/ring, and forward-triangle dynamic beam configurations, and correlating with melt-pool behaviour, microstructure, and mechanical performance. The core-only beam produced a highly concentrated heat source with limited melt-pool mixing, leading to Al accumulation (~2.7 wt.%), a high Fe(Al,Si) area fraction (~45%), and reduced linear joint strength of 211 ± 39 N/mm. The static core/ring beam did not significantly suppress Al enrichment or IMC formation due to the absence of temporal modulation. In contrast, the forward-triangle dynamic beam shape at 1428 kHz shape frequency promoted repeated beam traversal and enhanced melt-pool stirring, reducing Al content to ~1.3 wt.% and suppressing Fe(Al,Si) formation by ~78%. This was accompanied by martensitic refinement, increased low-angle grain boundary fraction, and improved hardness distribution. The forward-triangle beam shape achieved the highest linear joint strength (472 ± 26 N/mm) and weld efficiency (58%). Overall dynamic beam shaping effectively tailors melt-pool chemistry and solidification behaviour in overlap welds. Joint performance is governed by the combined effects of Fe-Al phase suppression and martensitic microstructural refinement enabled by dynamic beam modulation.