It sounds like the whole system has a huge public goods problem. In the real world stock market, buying TSLA is a signal that you believe the price is good, and if you're a big enough investor, your buy might move prices up before you complete. In this world, other people can steal that signal and move the price before your transaction even starts. Isn't this a design flaw?
There are ways to make marketplace contracts which allow buy and sell orders like this that aren't vulnerable to front-running. It's possible to have the buy and sell orders happen off-chain and then be settled on-chain later (Loopring works this way; there are other benefits to this system too such as speed of execution and lower fees), or for a marketplace contract to require orders to be preceded by a precommitment transaction, which includes a hash of the upcoming order, so the upcoming order can't be frontrun because the frontrunner would need to do their own precommitment transaction first.
Note that a marketplace contract like this isn't the only kind of smart contract; it's not the case that all smart contracts have the potential for front-running vulnerabilities. For example, there are smart contracts that do things like manage community funds and require people to vote on how the funds are spent, which don't do anything that could be vulnerable to front-running.
