People seem to be forgetting about Abbott, who in my opinion did indeed fuck around with rubbish policy his entire term (helped into the grave by treasurer/idiot Joe Hockey).
(1) The NBN falls under the portfolio, and the government knew they would have to deal with controlling the ever increasing costs of the program, which were hugely underestimated by Labour, and (2) The person in the role of Communications minister would take the blame for the public realisation that the costs were going out of control and had to be cut. (3) Any cut would result in a poorer NBN, because that's what cutting costs when you're building any product/service does.
So he was essentially handed that flaming pile of dog shit by Abbott, probably to lower the chance that Turnbull would ever be able to wrestle back power.
Turnbull's solution was to get the private sector to pay for a part of the network (FTTN instead of FTTH). So, costs would be managed, the 2020 target was still reachable, and it leaves the NBN open to improve the network to FTTH later on.
What could Turnbull have done better?
The bigger problem of the NBN is its business model, which charges Telcos for bandwidth on a total downloads basis rather than on a % use basis. This is what causes the poor service of the NBN. This could have been dealt with by Rudd, by using a different model for the NBN, as discussed above, but Turnbull couldn't do anything about that.
He has a slightly better grasp on some areas of technology than the average person perhaps, but certainly no more than the absolute bare minimum any communications minister should be required to have.
The problem with Turnbull appears to be that either:
1) He has to balance his rather more radically right wing members of his party while keeping his further centre members happy else he loses his position. (Many peoples explanation).
or
2) He has significantly changed his opinions and position on many issues over the last 5 years.
And this is a problem because people cant really tell which it is.
Turnbull hasn't really changed many of the policies of his predecessor, he just wraps it up nicer and in a more statesman like fashion.
He was previously a more moderate right wing (by australian standards) but has since gone significantly more right wing.
Im not going into specifics because I don't want to go beyond the realms of the overall topic and end up talking about Gonski or something, but thats my take on why people are a bit bemused by Turnbull and not particularly forgiving despite his inheritance.
I believe proposition (1), there being more evidence that supports this view and more rhetoric that supports (2).
If he were elected with a significant majority of both houses, and the party returned to a more centrist state, such that he didn't need to appease the more Right-wing faction of his party in the same way, would he not still be the perfect PM many of us thought he might be?
An aside -> his election strategy was mostly: (1) use data to find popular buzz-words ("JOBS", "GROWTH", "INNOVATION"); (2) repeat those ad infinitum; (3) shy away from any compelling political narrative or vision for the future of the country (e.g. "MAGA" narrative); (4) ???; (5) Lose House seats to Shorten and Senate seats to Pauline et al.