The trouble with claiming that there was no Battle of Hastings is that there still needs to be a reason as to how William I was able to establish himself as King of England in 1066, establish a largely Norman aristocracy in the shape of its Anglo-Saxon predecessors, enact a series of sweeping legal, land and church reforms, and still spend about 20 years consolidating power and clamping down on rebellions. And those means need to be somehow less palatable than 'I invaded, I nearly lost the battle but won eventually' in order to require such an extensive cover-up. The Battle of Hastings is attested to by such an extensive range of sources - from the Bayeux Tapestry to the Anglo-Saxon Chronicle to multiple contemporary histories (Guy of Amiens, William of Jumieges et al) and almost-contemporary writers (Orderic Vitalis, William of Malmesbury) that we know it happened in quite extensive detail. The lack of certain archaeological evidence is of no surprise whatsoever.

As an archaeologist with the best will in the world, finding archaeological proof of something is quite often completely down to the luck of the draw. Obviously, finding something like a castle or a Roman villa is more likely, but the survival of small artefacts, in particular metalwork, leather, bones or even whole bodies, is chance work. East Sussex is prone to acidic, watery soils which are the natural enemy of small, easily corroded things like iron arrowheads, spears, bone fragments and the like, assuming that the battlefield itself wasn't picked clean in the wake of the battle anyway.