A part becomes complex through its geometry, its tolerances or its material — often all three. The answer is rarely a bigger machine; it is a better process plan.
A DFM review first, then a process plan that minimises set-ups — 5-axis simultaneous where it removes re-fixturing, purpose-built fixturing where it stabilises a thin part, and staged machining where stress would otherwise move the geometry.
Often one complex part replaces a welded or bolted assembly: fewer parts, fewer joints, fewer leak paths and a shorter bill of materials.