It also assumes a relationship between burial sites and places of worship or spiritual significance which is typical of Christianity but not even universal among Judaeo-Christian cultures – Jewish kirkuts are not placed next to synagogues and I think the same is true of Muslim burial grounds and mosques – let alone the wider world.
But barrows surely can't have been the only burial sites; the skeletons in them are too few in number and too widely and sporadically distanced in dating. They must have been used for burying people who were in some way special: kings? wizards? priests? maybe the "cells" were exactly that and these were prisoners, left where they fell? Which then raises the obvious question of what was done with the rest of the dead. The barrows are very obvious structures, impossible to miss, which suggests some sort of importance – though it's possible the importance could have been "keep away, here are the dead!"
Warehouses seems unlikely to me. The internal space is so restricted compared to the overall size of the structure. Also, would any culture really bury its dead, however special they were, in a food store? Of course, that could have been a later repurposing; or these particular dead could have been food (but then where are the bones of other meat: sheep, pigs, etc – that you would expect in a meat store?).