WP:PRIMARYTOPIC holds that:

While Wikipedia has no single criterion for defining a primary topic, two major aspects that editors commonly consider are these:

• A topic is primary for a term with respect to usage if it is highly likely—much more likely than any other topic, and more likely than all the other topics combined—to be the topic sought when a reader searches for that term.
• A topic is primary for a term with respect to long-term significance if it has substantially greater enduring notability and educational value than any other topic associated with that term.

Discussion commenters have attempted to quantify this in discussions such as this (by User:SMcCandlish):

I suggest that WP:PRIMARYTOPIC needs some clarifications:

1. Incoming pageviews are not the be-all and end-all of the determination; sources are more important.
2. A slight majority of pageview preferences (e.g. in the 51-65% range) is never enough to establish a particular article as a primary topic, especially if source research suggests otherwise.
3. A pageview preference around 75% is not sufficient for something to be the primary topic when there are multiple notable things of the same sort (e.g. songs) by that name and we have at least three articles on them, nor when there is a large number of notable things by the name (e.g. more than 5). A 90% pageview ratio would indicate a primary topic in such a case, however, if the topic was not something very recent.
4. WP:RECENTISM applies, and Wikipedia does not move articles around on the basis of what is temporarily popular/notorious right now, which may result in sharp but short-lived pageview and news-coverage spikes.

However, in WP:ONEOTHER cases, one of the pages serves as both the primary topic article and the de facto disambiguation page by way of the disambiguation hatnote at the top of the same page. Readers seeking the non-primary topic only need one click to reach their destination from the primary topic page via the hatnote.

Consider the following two imaginary cases. First, a term with three meanings:

Pletskath may refer to:

• Pletskath (book), a 1679 treatise by Xenopath — 30% of pageviews
• Pletskath (animal), a two-limbed, cold-blooded marsupial — 60% of pageviews
• Pletskath, Wisconsin, a village east of Milwaukee — 10% of pageviews

In this case, all other factors being equal, Pletskath (animal) would likely not be considered the primary even though it gets a majority of pageviews. Instead, the base name would be a disambiguation page linking to the three articles. The result is that 100% of readers arriving at the disambiguation page would have to click once to reach their destination.

If animal page was/were moved to the base name, the 60% of readers seeking the animal article would reach their destination faster with the animal now occupying the base name. However, the 40% of readers seeking the book or the village would peruse the animal page more carefully and then have to click twice to get to their destination, once from the animal base page to the disambiguation page and then again to reach their final destination. (Think of it as 80 clicks per 100 readers versus 100 clicks per 100 readers when there is a disambiguation page)

Next, a term with two meanings:

Torrezhap may refer to:

• Torrezhap (city), a city on Ganges Island — 40% of pageviews
• Torrezhap (dance), a traditional Macronesian dance — 60% of pageviews

If dance article was/were moved to the base name, the 60% of readers seeking the dance article would likewise reach their destination faster with the dance article now occupying the base name. However, in this case, the 40% of readers seeking the city would only have to click once to get to their final destination, since there is no intervening disambiguation page, representing a much lower comparative inconvenience. (Now only 40 clicks per 100 readers versus 100 clicks per 100 readers when there is a disambiguation page)

Thus, since there is a greater comparative benefit, there is more utilitarian incentive to move the dance article to the base name in a WP:ONEOTHER situation. A 60% of pageviews threshold would likely be unacceptable to qualify a topic for primary status when there are three or more topics of that name, but could be acceptable if there are only two topics sharing the name.