Using the phone part is absolutely correct but any type of NBN connection has that risk, just Satellite and FTTP being more reliable in that sense as they can be battery backed up in the home to keep the connection as long as the backup power lasts. HFC, FTTN among others do not have this capability and NBN and RSPs recommend that a Mobile phone is kept for emergencies, they also recommend this for FTTP and Satellite.
So the issue isn't just with FTTN, not a great answer but the best that can be had at the moment. Keeping the copper lines is not a magic bullet either, the copper is failing as it ages, weather has a great impact on the connection, power to run it was/is not guaranteed (though it was very reliable). In all of this, Australia got what it voted for, no less no more. If the majority of Australian voters hadn't elected the LNP Federal Government we would have a very different and more resilient NBN for most Australians than we do now. I don't know if we would have any better connection speed issues as even under the Labor plan the NBN had to be a commercial success which meant CVC pricing would still be the biggest impact. With a great deal of money spent and much of the work commenced or contracted it would be a huge cost to redo it in one hit.
The speed drops are not the NBN infrastructure so much as it is the failure of RSPs to buy sufficient CVC for the number of customers they have at the various speed tiers. With on average only around 1.08 Mbps per customer (as at Aug 2017) there are times of the day/week/month that the service may slow to a crawl (depends on who your RSP is as some actually do buy more CVC). The big 3 (Telstra, Optus, TPG) tend to have the lowest CVC per customer, but it definitely is not isolated to them.
CVC is the biggest monthly cost for a RSP and so to make their bottom lines better they tend to buy the least they can get away with. In June 2017 there was a price change to the CVC cost (lowered) the more CVC was purchased by an RSP, this change to the way CVC is priced has seen CVC purchases climb a bit but as more people take up access this increase has been diluted in it's impact on the users.
The NBN CEO wants RSPs to increase the average CVC available from the current average 1 ish Mbps to around a 2 ish Mbps to improve the customer experience. To do this would obviously increase the costs to RSPs which they would then pass onto their customers by increasing plan costs (this could be a significant increase per user).
To read a news article on it see:
How to get it fixed? Well the CVC issue is being looked at by the ACCC so as a user I encourage you to contact the ACCC with your complaints, write a complaint to NBN Co, write a letter to your newspaper, continue raising the issue on sites like Choice and Whirlpool, start a petition, contact your Federal members and let them know about your disappointment/anger/frustration (leave them no doubt about how their next election result might ride on their efforts). Contact your RSP and let them know and if you suffer from the connection issues lodge a complaint with the TIO. Not all this will bear fruit nor will they probably do so quickly if they do (but you never can tell), but they will lead to improvements if enough people do take action.