Sure it could: 1 or more casters casting from concealment- or possibly using things like still spell or silent spell, or items- to avoid detection, with a team of urchins to do the mid-stampede grabbing.
Thievery of this kind often involves teamwork.
The more resources you are collecting to perform the job, the more problems you have. Teamwork and coordination on that scale is hard and requires a lot of practice. You also need a bigger payout to pay all your participants. If you have a team of that size, you are essentially talking a whole thieves guild pulling the scam. This scam is flashier, but it's arguably not more effective than hitting the target with a similar sized team of all rogues with appropriate tradecraft. If you are talking about something like a silent still major image, you've got to have a 9th level wizard to pull that off. If you have teams of 9th level wizards equipped with magical items to pull this off, backed up by some 5th level wizards, backed up a bunch of 1st level rogues, you could pull the same crime as a standard armed robbery with an equivalent team of leveled fighters - multiple 9th level fighters, multiple 5th level fighters, and a bunch of 1st level fighters could roll most small town city watches with relative ease. So again, basically you are talking about a large force of bandits at this point. Eventually yes, you'll have enough magical prowess to roll a marketplace by brute force. Forget silent still major image to create panic, you might as well be telling me how a team of 9th level wizards with wands of lightning bolts and appropriate retainers could rob small towns. Yes, probably so. I'm not expecting a small town to be able to defend against that much concentrated force.
Your team is going to draw a bunch of attention. I mean, in my campaign world, the players started play in the city state of Amalteen - roughly 300,000 residents. In the entire country, there were only 2 characters above 9th level. Pulling off a stunt like that where multiple 9th level characters were pulling off wondrous feats would become a rumor of regional scale. Millions of people would soon be talking about this rumor. Several major cults would intervene, as would the nation state itself. It might be a fairly even match, but your team of crooks would be a regionally important BBEG. Similar things are true of the real world. If you hit a gem trade show with enough force to pacify a target of that size for a grab job, you'd make the national news and have the FBI all over you.
Pulling this off with a team with slightly less force is possible, but if you do, the amount of force required to stop you is equivalently less and the amount of coordination needs to be even higher and more perfect. You'd get away with it a couple of times, but eventually enough would go wrong that you'd be in trouble. It would be similar to the bank robber periods in the 1870's or 1930's. Things would either go wrong by chance, or you'd run into an ambush where they set you up and things would go to heck in a hurry.
By comparison, if you have 1 5th level wizard with this reserve feat there are no obvious counter measures. The closest equivalent I can think of is in the 1990's, when they first figured out that you could use LED's to confuse the coin counters in slot machines and a single grafter with a light stick could walk the strip pulling a few hundred from each casino and make $5000 a day with basically no chance of being caught until the casinos worked out what was going on (mostly because some guys got too public with it). Guys were pulling $1 million a year out of the casinos with almost no skill required. If that had kept up, if there was no counter measure, they would have just closed the slot machines down.
Fifth level wizards are fairly rare in my game, but they are not that rare. In my game, many of them are 'hedge wizards' - essentially working tradesman. If you could learn a trick like this? In my opinion that changes the entire culture of the world. There might be only one 10th level wizard in the 300,000 people of Amalteen, but there are probably 180-200 5th level wizards. Your 'scare 'em with spells' model is basically just banditry by wizards, and bandits are a problem but they have short life expectancies and are a known factor with all the sorts of countermeasures you can employ against bandits. This? This is walking out the door with anything left unattended, and I can't think of countermeasures in a world that is actually pretty thick with counter measures (those hedge wizards mostly make their living selling things to defend against magic). A couple dozen wizards learn this trick to be able to earn easy money? Yes, it changes the culture of the entire nation.
One of my
other hobbies* is jewelry design. I get a lot of my raw materials from
Intergem trade-show vendors. The setting is essentially an indoor bazaar, with 100+ vendors with their wares set up on tables and some in locking cases. Typically, there will be 2-4 people working an average booth.
My mom works jewelry shows in the Texas to Missouri area. Not sure if she visits the same shows. But she sells jewelry and buys some of her stones from vendors. Most of her stones though are from rock hounding though. My dad does cabochons and polishing of native stones - agates mostly.
Why use this feat when a Major Image or a summoned lion will net you a bigger haul?
I don't buy it. One illusion or one summoned creature is not going to net you a bigger haul without all that backup and help you mention. Even with that back up, you are going to have problems. It's the difference between trying to hit a casino and pulling a con on one. The kind of jobs you are talking about would require case work, planning, escape routes, cover stories, fronts operations, and logistic support. You've got a team of dozen people doing the front work, many of them kids. There is so many dang things to go wrong here, and covering up your trail is going to be a pain in the rear. I wouldn't even have to invent anything to stop the PC's. If they could run this operation, they'd earn their levels fair and square, but just the standard sorts of obstacles they'd have to overcome... I wouldn't expect most players I've gamed with to run it perfectly enough to keep in business.
This feat? Only an idiot would get caught.