The improvement in the squad has been astronomical, and almost certainly unprecedented. No other Rangers manager has overseen such an improvement in a squad he's been in charge of for two years.
While the chances of Gerrard leaving were probably slim, results in March 2020 probably meant a similar season wasn't going to be enough to keep him. He had to oversee a much more pronounced level of improvement than be brought between 2018/2019 and 2019/2020 - and he did. There's genuinely nothing lost in wondering at the time whether he was capable of that - it actually makes this year's success all the greater.