I haven't heard "Hold Your Banners High" before, except for the version that Grimethorpe Colliery Band recorded, and you can hardly expect the band to be able to do anything simelar to that.
I do, however, know the recording of "Lay Me Low" on the Albion's album Rise Up Like the Sun. The arrangement the band performed at Sidmouth wasn't to vastly different to the recording. The vocal lines can't be replicated without at least half a dozen more singers, like they had on the recording. You're right, the arrangement of the vocal parts, and contrast of the upper and lower parts in different choruses is terrific. But what John Tams and the band did at Sidmouth was perform the song with great passion, and that's what made such a memorable performance for me.
Perhaps you've seen John Tams on better form, on other occasions. I haven't: that was the first time I'd seen him. I didn't think the set was short, either: it certainly didn't end early, did it?
If you didn't much enjoy their set, I hope you prefered Pete Morton's, in the first part of the concert. He's the only person I've ever heard sing "To Be a Farmer's Boy" and make it sound fresh!