Putin could end it by pulling out and returning the civilians. Of course, it would mean that he's probably going to lose power, and also he believes he's smarter than everybody else, and would never admit he made a mistake, so he's going to double down.
I see it as the opposite - the US (and NATO) has been steadily increasing aid based on the capabilities of Ukraine to support and efficiently (and safely) use what we give them. We worked within the limitation of training their standing army with what they possessed and would have immediate access to, which was mostly Soviet-era equipment.
We also needed to know that if we shipped them an expensive weapons system, that they would use them properly (and not simply be dropping expensive rounds on open fields because somebody wasn't programming coordinates properly) and more importantly they wouldn't immediately lose it to the Russians (whether by capture or air or artillery strike). We damned sure couldn't start dropping in F-16s if there was a chance that the Russians would immediately knock them out with missiles/air strikes, we needed to make sure that the Ukrainians could keep their own Air Force running.
In terms of your examples - Abrams and Bradleys and F-16s each require a hefty repair/maintenance/logistics chain that we've had in place for well over four decades - that's a shit-ton of institutional knowledge that is passed down from mechanic-to-mechanic, in training schools that have four decades worth of expensively-learned knowledge. And that's before we talk about training people to use them.
Don't get me wrong, I would have liked it if we took Ukrainian pilots and started getting them up to speed on F-16s back in March, just in case, but NATO has enough Soviet aircraft for now that we can push into the Ukrainians, and then backfill those NATO nations with F-16s. That would be easier for us to help supply and get up and running in a country where we can have boots on the ground looking over the shoulders of their mechanics and pilots, versus pushing them into Ukraine, where our personnel would not cross the border and couldn't do hands-on help.
We also can't just stand up Abrams, Bradley, and F-16 maintenance/logistics support infrastructure in Ukraine, where it was completely staffed by Ukrainians. Abrams run on turbines, which would slow down Ukrainian mechanics used to the engines of Soviet equipment, and they share no parts with the Soviet T-series. Our F-16s share no parts with Soviet aircraft, etc. and we would have to move a massive amount of spare parts and ammo into Ukraine as well, and those would be fixed locations, prone to attack by Russian air. There's also a reason why we stockpile that equipment and weapons in Europe, the Pacific, and Middle East, because it's not easy to move that much gear that quickly, as good as our airlift and sealift are.
With that said, We have been steadily helping to build up a Ukrainian military that is poised to go on the offensive, up to and including the taking of Crimea.
We have been training tens of thousands of their soldiers, we have been providing extremely expensive and accurate artillery (both barrel and rocket), we are working with them on unmanned water-based vehicles that in theory could take out their ships/subs sitting at anchor. We have been providing more and more anti-air defense (AGM-88s, etc.), and now that much of their cruise missile capacity has been eaten up, all the while we are boosting their anti-air defenses, today NATO shifted their priority to countering drones as well. These things are meant to help Ukraine proper in dealing with Russian air attacks, but also help the Ukrainian military focus on their offensives.
I'm not saying that our aid has been perfect, but there should be plenty of case studies written about this, because everything we have provided has been put to extremely good use, so whatever we are doing in terms of training and supplies is working.
And it's working well - Russia is having to resort to buying weapons from fucking Iran, bringing 60 year-old tanks out of retirement, and they are literally kidnapping random men off the streets to fill their ranks.