The tower proposed for Market Street and South Van Ness Avenue hasn’t even been approved, but it’s already raised the bar for how developers and architects pitch big buildings in the San Francisco of 2019.

The 590-foot residential tower would include sky gardens to “integrate nature with urban context,” its developers say. They also promise the city’s “first carbon-neutral high rise,” and only 246 parking spaces would accompany the 984 apartments. Add maker spaces and $13 million for affordable housing, and what’s not to like?

Or, to take with a grain of salt. Because as the next batch of proposals comes in for the area that city planners are calling “the Hub,” the simple truth is that it will take more than big buildings to improve the quality of life in this busy but problematic civic crossroads.

Strip away the hyperbole, and 10 South Van Ness represents the biggest tower proposal yet for the Hub.

The area includes roughly 14 square blocks along Market and Mission streets on either side of Van Ness Avenue. For decades it has been a throughway rather than a destination, a patchy void with attractions such as the Zuni Cafe and the Green Arcade bookstore but also its full share of troublesome social conditions.

Now, a 39-story apartment tower is under construction on the northeast corner of Mission and South Van Ness, while across the way at 30 Otis St. the site has been cleared for a 26-story apartment building. And city planners want to go further — the area is being studied for a rezoning that would allow three towers in the 600-foot range at the vast intersection of Market, Van Ness and South Van Ness.

The idea behind the extra development is to bring a number of other improvements, such as landscaped sidewalks and plazas, while generating fees that would help fund road, transit and bicycle improvements. Of the 1,700 or so additional housing units within the proposed changes, one-third would be required to be priced at affordable levels.

Environmental studies for the Hub plan are now under way. The final hearings and San Francisco City Planning Commission votes are not expected before late this year.

The 10 South Van Ness proposal, which was presented this month to the planning commission on an informational basis, takes its cues from the guidelines in the works.

The developer is Crescent Heights, which in 2015 proposed a pair of 40-story towers for the small triangular block bounded by Market, Otis and South Van Ness that for decades held a Honda dealership. The updated proposal comes with one tower instead of two and a new architectural firm, Kohn Pedersen Fox.

In the abstract, the revised concept is beguiling.

The design has a triangular base topped by a single tower with four shallow wings arranged pinwheel-like around a central core — a bundled approach that aims to diffuse the strong afternoon wind. Each wing would be punctuated by a three-story sky garden to also muffle downdrafts to the sidewalk (and yes, create amenity spaces for tenants).

Roughly 190 of 984 apartments would be reserved for lower-income residents. The efforts to reduce carbon emissions in the tower’s ongoing operations are substantial enough that the state has classified 10 South Van Ness as an “environmental leadership development project.”

But you don’t have to be an anti-growth zealot to be wary of the notion that quantity and quality are synonymous.

At the most basic level — the base — the presentation included images of an enclosed through-block arcade, lined with fashionable cafes and shops. The architect suggested it could play a role similar to the Ferry Building. A better comparison might be Crocker Galleria, which opened in the 1980s in the midst of the Financial District’s towers. It languished when downtown retail was buoyant and is even bleaker now.

As for the promises of a “thriving mixed-use residential project for people to live, shop and play,” Crescent Heights’ local track record is mixed at best.

Most storefronts in the developer’s NEMA tower at 10th and Market streets are vacant, despite having 754 apartments above them. Crescent Heights received approvals in 2016 for a 48-story tower on Howard Street alongside the new Transbay Transit Center, but nothing has happened.

Nor is there any sign of action at the corner of Market and Van Ness, where the Hub’s first tower proposal, the 40-story One Oak, proposed by Build Inc., was approved in 2017.

Fortunately, the two Hub sites where construction has begun show promise.

Furthest along is the 1500 Mission St. project at Mission and South Van Ness. Designed by Skidmore Owings & Merrill, it will open next year with a 39-story, 550-unit apartment tower at the corner and a 16-story building filled with city government workers framing it to the east and north, with pedestrian passages in-between.

The tower’s bones are now 16 stories high — and the angled profile, with the precast concrete skin parting as it rises from the corner, already brings a welcome visual accent to the daunting intersection. The one awkward touch is the 26-foot-wide passage on Mission Street between the tower and the city building. The dimensions seem pinched, though things might snap into focus when the complex is complete.

As for 30 Otis St., where construction should soon start, the design by Gould Evans calls for a 26-story tower with an exposed concrete frame rising from nine-story masonry-clad wings on either side. The section along Otis Street would step down toward the alley behind it, allowing sun to reach into the block.

By including City Ballet as the main tenant, developer Align Real Estate holds onto an institution that occupied a smaller space on the site. The adjacent theater would widen the net of cultural spaces that now reach beyond Civic Center to the west and south.

The other element is a small plaza at Otis and 12th Street that would be designed by Mexican architect Frida Escobedo working with Fletcher Studio, one of the city’s best landscape architecture firms. Her plaza is conceived as a flowing set of informal rooms that could hold everything from cafe seating to small events.

This is a far cry from 12th Street’s current state, with a blank wall on one side and a homeless Navigation Center on the other. Nearby side streets and alleyways are no more enticing.

In the long run, the ambitions for the Hub make sense. The two projects taking shape offer the right mix of buildings, activities and public spaces of varying scales.

But the duo is only a start.

The mammoth intersection of Mission, Otis and South Van Ness needs to be tightened so that people on bicycles or on foot aren’t afraid to cross it. There needs to be an ongoing effort to improving the area’s grim social conditions. Officials can’t just assume that new development will make everything OK.

Proposals like 10 South Van Ness will be packaged as magic bullets to cure all ills, but they must be seen as part of a larger puzzle. Otherwise, we’ll be left with visions that look great in renderings but never come to pass — or turn out to be the architectural equivalent of a bait-and-switch.

John King is The San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron