It certainly is excessive and in normal use very little tread in contact with the road during braking. Though I have seen almost the same degree on vehicles used in stock car and banger racing in the past on short oval circuits, though I imagine they would be rubbish on normal roads.
In those days the "Banger boys" used to fit s/h racing tyres to their bangers and put a cut down old standard tyre band without the tread area on the outside so from a quick inspection they passed scrutiny, but handled much better than others when racing due to the soft racing tyre being all that touched the tarmac
I once put a small amount of negative camber on the front suspension of a Ford Anglia and immediately noticed an improvement so when doing spirited cornering it eliminated tyre squeal, even with the original 5.20x13 crossply tyres, so with the Dunlop 5.5 J steel wheels and Uniroyal 175x13 tyres I noticed a marked improvement.
The one mod I quickly removed was the stiffer twin antiroll bar conversion some recommended.
The car was already lowered front and rear, so for a apprentice on low wage it was a fun form of transport.
Re the boys in blue in those days we would get pulled, but generally only got a bit of firm advice rather than the penalties etc. of today.
I recall being followed for over a mile and finally pulled over for some strong advice regarding a spotlight bar made of angle iron, if the previous owner had not kept the spotlights it would have been fine, but officer rightly said if I had knocked anyone over it would have caused more damage so I removed it.