Are you a construction expert ?
The " Great Tunnel " was 100 meters long and 9 meters deep. This one was only 30 meters long. Another escape tunnel with about the some measurements - 30 meters long , with no wood support , was also dug in Stalag Luft III . So much for your argument ...
" Lieutenant Michael Codner, Flight Lieutenant Eric Williams and Flight Lieutenant Oliver Philpot, in shifts of one or two diggers at a time, dug over 30 m (100 ft) of tunnel, using bowls as shovels and metal rods to poke through the surface of the ground to create air holes. No shoring was used except near the entrance.
A tunnel reportedly ('Evidenced' by testimonies only? Again?!)
shored up only "near the entrance
," is this the best you could find??? C'mon !!
From the link you provided:
The tunnels were very deep – about 9 m (30 ft) below the surface. They were very small, only 0.6 m (2 ft) square, though larger chambers were dug to house an air pump, a workshop, and staging posts along each tunnel. The sandy walls were shored up with pieces of wood scavenged from all over the camp, much from the prisoners' beds (of the twenty or so boards originally supporting each mattress, only about eight were left on each bed). Other wooden furniture was also scavenged.
After the escape
Following the escape, the Germans made an inventory of the camp and uncovered how extensive the operation had been. Four thousand bed boards had gone missing, as well as 90 complete double bunk beds, 635 mattresses, 192 bed covers, 161 pillow cases, 52 twenty-man tables, 10 single tables, 34 chairs, 76 benches, 1,212 bed bolsters, 1,370 beading battens, 1219 knives, 478 spoons, 582 forks, 69 lamps, 246 water cans, 30 shovels, 300 m (1,000 ft) of electric wire, 180 m (600 ft) of rope, and 3424 towels. 1,700 blankets had been used, along with more than 1,400 Klim cans. Electric cable had been stolen after being left unattended by German workers; because they had not reported the theft, they were executed by the Gestapo. Thereafter each bed was supplied with only nine bed boards, which were counted regularly by the guards.
Shows very well how childish, fanciful & extravagant this specific Holocaust tale is, doesn't it?