I what it accomplished, what Jager is saying is that it was more that just short bowling aimed at the body with a predominantly leg side field with the intention of hurting the batsmen or getting them to play the ball to leg in the air.
This was the effect, not the intention.
In 1928/29 England, with Jardine a junior member of the side, won the Ashes 4-1 - the pitches were perfect for batting, prepared for timeless Tests, and the going only got tough if it rained and the wicket turned sticky
In 1930 Bradman changed the natural order of things - Jardine and England believed on 1928/29 pitches, which they had every reason to expect again, that they simply would not be able to get him out.
Fast leg theory was designed to stop Bradman in particular but the Aussies in general, from scoring as many runs so quickly - the idea was if you bowled fast, short and to the leg side and packed the leg field then the batsman either couldn't play a shot at all (and therefore didn't score), backed away to leg to try and force through the vacant off side and thereby take a big risk, or take an equally big risk by scoring runs through the areas where all but one of the fielders were.
No one set out to hurt the Australians - that they got hurt was because in fact the bounce on the wickets, unlike 28/29, tended to be uneven so they couldn't be sure the short delivery wouldn't stay low and hit the stumps, so the slow footed ones like Ponsford, Woodfull and Fingleton preferred to get hit rather than risk being bowled or lbw to one that kept low
Bradman tried the off-side route with some success - he only got hit once in the series, by Larwood on his backside
McCabe tried the leg side route with one spectacular success, his famous knock where he flayed Larwood and Voce and nearly killed the tactic, but he did little after that
There was another way for a Test class batsman to play it - stop whining, stand up straight, get in line and wait till the bowlers tire themselves out - the Aussies didn't try that - but Jardine demonstrated how to do it against Constantine and Martindale at Old Trafford in 1933