The 49ers have done well in free agency, but there’s still one glaring hole remaining

Good NFL teams don’t build through free-agent splashes.

No, big free-agent spending sprees are typically the domain of the Jets, Raiders, and Jaguars.

The is to acquire good players, mainly through the draft, and to keep them around when their contracts are set to expire. Then you can augment in free agency.

That’s what the 49ers did during this free-agent period. They deserve plaudits for keeping left tackle Trent Williams, cornerbacks Jason Verrett and Emmanuel Moseley, and fullback Kyle Juszczyk and adding pass rusher Samson Ebukam as a Dee Ford replacement (even though Ford remains on the roster) as well as upgrading the center position by agreeing to a deal with former Cal Bear Alex Mack.

The 49ers did what good teams do.

Everything the 49ers have done in free agency has been solid. But it’s the move they have not made to date that could prove critical to their goal of returning to the playoffs in 2021.

Let’s be clear: The Niners’ 53-man roster inspires confidence. They have elite players at left tackle, defensive end, linebacker, tight end — this team has some serious dudes and an underrated amount of depth, which will only be added to with a good draft in April.

But the Niners had a good roster going into last season, too. And while injuries hit every area of the team, it was quarterback Jimmy Garoppolo’s sidelining that derailed San Francisco’s season.

Garoppolo signed a fiveyear, $137.5 million deal

ahead of the 2018 season. Since then, he’s missed 48 percent of the Niners’ regular-season games. And, to date, the Niners have not ensured a viable way to win should Garoppolo miss time again in 2021.

It makes some sense as to why the Niners did not sign a backup quarterback amid the first wave of free agency — Andy Dalton, Tyrod Taylor and Jameis Winston all landed eight-figure deals. The Niners couldn’t afford that — not if they wanted to keep Williams, who agreed to the largest deal in history for an offensive lineman, a six-year, $138 million contract.

There are only two quarterbacks who remain on the market who

could, in theory, win games in the absence of a bonafide starter like Garoppolo. How much confidence would you have in riding with Alex Smith or Mitch Trubisky, two players that have not been in a Kyle Shanahan/ Gary Kubiak-style widezone offense?

Neither quarterback is likely to land an eight-figure salary for 2021, but they won’t be dirt cheap, either, and the Niners are pressing up against the cap when you take into account the money they have to spend on draft picks and necessary inseason cushion.

And trading for Sam Darnold from the Jets won’t solve that problem — his cap hit is $9 million

this season.

There are a million ways for teams to massage and manipulate the salary cap, but the Niners’ serious spending is likely over.

Meaning that it’s unlikely they add someone with a worthwhile NFL track record, unless that player takes a steep discount.

Right now, all signs point to the Niners continuing to try — fruitlessly, it should be noted — to land Deshaun Watson from Houston or entering the crapshoot that is the draft.

One could make the argument that all these big contracts the 49ers have handed out in recent years — and the contracts

they’ll need to hand out to Nick Bosa and Fred Warner in the years to come — will force San Francisco to go cheap at quarterback going forward.

It’s not a bad thought, but San Francisco would have to be all-in on the youngster, and no one can guarantee a rookie quarterback will be successful in the league.

If the Niners use their first-round pick (they’d likely have to trade up from No. 12) to select a quarterback in April, that’s not only the team’s backup this season, but he’s also the team’s starter in 2022.

Hope they pick the right one. Otherwise, they won’t improve their position at all.

For a team that believes it can be a Super Bowl contender with Garoppolo, it’s a big leap to apply the same logic to a rookie quarterback — much less one that isn’t the best in his class.

But that’s what the 49ers would be doing.

Maybe they land Watson. That’d be something. Maybe Trubisky signs a super-cheap deal with the Niners. That’d play. Perhaps Garoppolo stays healthy for the entire year.

But absent any of those things happening, the Niners are leaving the quarterback up to chance in 2021 and perhaps beyond.

And we’ve seen how that’s played out before. It’s not pretty.