" bad grazing practice is entirely responsible for bracken spread."
A bit of a simplification. Upland grazing density is largely controlled by EU diktat. This led to compulsory de-stocking in the past and some argue grazing quality diminished as a result. In Ireland a minimum stocking density on commonage is required to comply with commonage framework plans.
If you cannot spray bracken, or access an area with machinery, stock trampling is the only tool left. On a free range upland no animal is going to look for grazing under a sterile stand of bracken. Therefore the bracken runs rampant apart from odd tracks made by sheep wandering from one gourmet grazing to another.
Uplands are completely artificial landscapes in the UK. The highland clearances and enclosure acts ran off all the smallholders and cottagers or their equivalent and sheep took over. They have largely monopolized the uplands ever since and the vegetational types present are directly controlled by the grazing regime. Without grazing the moors would be transformed within 2 generations.

randd.defra.gov.uk/Document.aspx?Document=BD1226_3897_FRA.pdf