The 100,000 mile service includes the first coolant change, I have performed that procedure a hundred times, the cooling systems are fine, no damage. Toyota’s Super long life coolant has been in use for 15 years and is many times better than the coolant we used 40 years ago.
There are millions of Toyota/Lexus vehicles on the road with 10,000 synthetic oil change service intervals, if this is no good we should have seen engine failures 8 years ago.