At an individual level, casualties in World War I were immense, and the cumulative risk of combat death or disabling injury for someone who was in service before the beginning of the war was far higher than had been experienced in prior British wars. I do wonder thought about TOTAL deaths, given the huge rate of deaths from disease that occurred in past continental adventures.

At a tactical organizational level -- the rate of casualties was such that many long-standing Army battalion and even regimental organizations that went into combat were fairly quickly red-lined (too many casualties to operate as an effective unit, even with replacements). These organizations were of course reconstituted behind the lines, but were substantially new, and also diluted with vast number of new organizations created for the purposes of the wartime army, as well as the interposition of divisional and corps organizations / commands that had previously been unnecessary. To call this "wiped out" might be a bit extreme.

Finally, thinking about the institution -- it doesn't take many survivors for a tradition-laden bureaucracy to continue and then restore itself. The Army of 1919 was very much the Army of 1913 in its constitution, tradition, regimental organization, etc., even if (of course) it was radically different in its technological, strategic, logistical and tactical footings.