He re-wrote songs - so?
He created songs and tunes from various sources - so?
He wasn't entirely up front about what he did - that is what, from an academic perspective, dis-credits all the rest of what he did - so?

So he lied. So he 'collected' material that he'd written himself, and lied about how he'd collected it and who he'd collected it from. Collecting is partly about getting songs down and putting them back into circulation, and partly about tracing songs back to their roots (or a little closer to their roots). Bert Lloyd did the first part extraordinarily well, but his contribution to the second part seems to be, well, a bit mixed.

If anything, he made it harder to document songs like Reynardine, The Recruited Collier and the Blackleg Miner: was there a pre-1808 version of TRC? was there a J.T. Huxtable who was singing it in Workington? was there a Tom Cook who was singing Reynardine? The answer seems very likely to be no in all three cases, but at this distance we can never be sure. (And was there a W. Sampey of Bishop Auckland who was singing the Blackleg Miner in 1949? I'm starting to wonder.)