Competing against a market leader with a twenty-year-old domain, a large content team and a national brand budget is a genuinely difficult position, and most advice for it is unhelpful. "Create better content" is true and useless when the incumbent creates a great deal of content and has authority you cannot match.
The approach that works is not to compete on the same ground. It is to be undeniably better on ground the incumbent does not care about.
Find the queries the leader is not serving well
Large competitors cover broad, high-volume topics thoroughly and specific ones badly. Their pages are written for a national audience, which means they are generic about location, vague about price, and silent on edge cases.
Your opportunity is in the specifics: particular use cases, particular industries, particular regions, particular problems. Individually these have low volume. Collectively they add up, and they convert far better than broad terms because the searcher's situation is unusual enough that a generic answer does not help them.
Be the most useful source on a narrow subject
Authority does not have to be site-wide to begin with. It is easier to become the recognised best resource on one narrow topic than a moderate resource on twenty.
Pick something you know genuinely well, where the existing coverage is thin, and cover it more thoroughly than anyone else has. That single body of work earns links, gets cited, and gives the rest of your site something to be linked from. Then pick the next one.
Publish the things a large company cannot
Big organisations have legal review, brand guidelines and reputational caution. That prevents them publishing real pricing, honest comparisons including their weaknesses, opinionated positions, and specific detail about how the work is actually done.
You can publish all of that. It is the clearest differentiator available to a smaller business and it is regularly wasted on the same cautious marketing copy the incumbent produces, only with a smaller budget behind it.
Earn links by being worth citing
Link building for a challenger brand works when there is a reason to link. Original data from your own operations, a genuinely useful tool or calculator, a strong opinion in an industry conversation, or the definitive explanation of something niche.
Awareness and links tend to arrive together when the underlying asset earns attention, and there is a practical set of approaches to that in this guide to creating awareness and generating leads. The common thread is that the asset has to do something for the person sharing it.
Use your size as an argument
Faster response times, direct access to senior people, willingness to take unusual jobs, no account management layer. These are real advantages and they are what buyers frustrated with the market leader are looking for.
Say so explicitly on the pages where people are comparing options. A comparison page that treats the incumbent fairly and then explains who each option suits is more persuasive than one that pretends they are not good.
Accept a longer timeline on the head terms
You will not out-rank an established competitor for their main term this year, and planning as though you will produces a strategy that fails everywhere at once. Concede the head terms for now, build revenue from the specific ones, and let authority accumulate.
The businesses that get there do it by compounding small wins over years, not by finding a shortcut.
Get the sequencing right
The main risk for a challenger is spreading limited resources across too many fronts and being mediocre everywhere. Choosing what to concede is as important as choosing what to pursue, and it is a judgement that benefits from someone who has watched the pattern play out before.
That is the argument for bringing in a specialist SEO agency in Adelaide or whichever market you are fighting in - not because the tactics are unknowable, but because the order you attempt them in decides whether a limited budget produces a result or a scattering of half-finished projects.