Brake component wear . How do you measure it ?

Other half's car is a gently driven 18 plate Ecosport Mobility car with 8k miles on it . It has been in to ... I won't name them yet ... for an issuue regarding the offside rear indicator flashing fast when you press the brake pedal  . 

While they had it in they did a 'compulsory' health check . They even sent her a video explaning what they were seeing . They explained three of the tyres were like new with 8mm of tread . Nearside front was needing replacing with 5mm/2k miles remaining on it . Dunno how they work that out . In my experience a tyre will do a great deal more than 5k with 5mm remaining . 

More concerning to me is that they said the front brake discs are 65% worn . Vented discs . Just as an example  and simplicity. If a vented disc was 10mm thick .. Lets say the braking surfaces were 3mm thick and the width of the fins were 4 mm think ... 65% of that 10mm overall width of the disc would be 6.5mm and that means more than the combined thickness of both the braking surfaces . If it was both surfaces worn the same it would be like the pads grabbing a propeller if you pressed the stop pedal . 
They replaced the pads regardless . . She didn't know they had until I had a look and told her . I have had a look and the discs do have a tiny lip on them .5mm  is my guess but i am being very generous at that .     .5mm on each surface of a 10mm disc would be 10% worn . 

She is proper worried and thinks her car is not safe to drive because of Jason at Ringways and his Mobility milking machine . 

Have had similar issues at EH in the past . A 10k miles  car that went through four sets of tyres and three sets of discs and pads . A three week old car that needed two new tyres because one was punctured . 

Anyone got the number for that 'Don't get done get Dom' bloke ?