Ask which is better, ads or optimization, and you will get an answer shaped by whoever is selling. The honest version is that they are different instruments, and the choice is about time, not money.
Paid placement is rented. It starts within hours, it is measurable to an uncomfortable degree of precision, and it ends the moment the card stops clearing. Optimization is owned. It takes ninety days before anything meaningful happens; it is hard to attribute cleanly, and it keeps working after the effort stops.
Where the ROI argument usually goes wrong
Paid campaigns win every short-window comparison, and they should — you can see the cost per acquisition by Thursday. Optimization looks worse on any report that closes inside a quarter and better on any report that spans a few years, because the denominator keeps shrinking while the traffic does not.
The mistake is running the comparison once, in month two, and treating the result as permanent. A business that has only ever bought its traffic has no asset at the end of it. A business that has only ever optimized has no way to move quickly when it needs to.
Volume is not the same as relevance.
The other thing owners misjudge is which terms are worth having. A phrase with a hundred and fifty searches a month sounds like nothing next to one with fifty thousand, and can be worth considerably more, because everyone typing the first one is trying to buy and most of the people typing the second are trying to learn.
Ranking for a small, specific term with a substantial piece of content behind it beats a page of general claims competing against every company in the sector. That pattern has held for a decade, and it is only getting stronger, because the systems now answering these questions are looking for the thorough source rather than the popular one.
The practical combination
Use paid placement for what it is good at: entering a new market, testing whether a message works before committing to content around it, and covering the gap while optimization takes hold. Use optimization for the terms you intend to be still winning in three years.
And do not neglect the unglamorous half of it. A site without a valid certificate gets flagged as unsafe before anyone reads a word of the copy, and no budget on either side of this argument can recover a visitor who has already pressed back.