你的两个句子都没有问题，即原句是对的，改写后的句子也是对的：
正：John’s salary as a bus driver was much higher than that of a teacher.
正：John’s salary as a bus driver was much higher than a teacher's.
约翰是名汽车司机，他的工资比教师的工资高得多。
又如：
A grandparent’s job is easier than that of a parent. 祖父母的任务比父母的任务要轻松一些。
The mindset of that generation was definitely more obedient than today's. 那一代人的思维模式比现在的人的肯定要更顺从。
下面摘录PEU一个例句：
