While mine is a R51 not an R52 I'll comment anyway
I think longevity depends a lot on peoples standards.
Tires w/ tread-wear warranties often neglect the fact that the internal carcass often declines before the tread does.
One giveaway is if tires are hard to balance or lose balance quickly need replacing even if treat looks good.
I agree w/ you that 30,000 miles is a proper life time for most OEM tires.