That's not a formula. That could work one year. Fail the next 2. Work the next 3. Fail the next 3. Could a person build a career on those results? A formula measures success against criteria.
Value and growth investors utilize financial history (balance sheets, income, cash flow) utilizing formulas to measure intrinsic value for future success because the formula has a high probability of returning consistant sustainable results over the average of time. Same with poker players. Same with businesses across industry. There are verifiable and measurable ways consistant with high probability of success.
When does one conclude it is skill and not sheer variance. What is the formula. How many trades over how long a time period with what percentage profitability? Sports betting has 55% to 70% profitability over X number of bets. Poker 5BB for every 100 hands over 100,000 hands to ensure it is skill and not variance. Just because it has not been mentioned, or has not manifested, does not mean it cannot be. It just means it has not yet been quantified.
Actually, in typing this reply I'd almost think sports betting may be the closest formula. They use signals and models and choose based on the most likely outcome. They deem 3000 sports bets, with 52.38% (to overcome the juice) profitability, the minimum needed to consider it skill vs sheer variance. However, with sports betting you win 1X your amount or Lose 1X your amount and pay juice on the bet (akin to moneymaker spreads). In trading you may risk 1% to win 1% to 2% or more depending on your strategy.
I would say it is fair to count an entry as one trade and an exit as a different trade. Both require skill in and of themselves, even if it's a stop out, because correctly setting your stop is just as important. If a person traded 2 round trip trades a day (4 trades total) whether in the same stock or multiple, 5 days a week that would equate to roughly 1,000 a year. So roughly 3 years of trading 2 stocks a day with a profitability of
X = Final Value
W = Expenses (taxes, spread, commissions, margin interest etc)
Y = Win Profit
Z = Loss Profit
Y - Z - W = +X after 3,000 trades (minimum) verifies skill and not luck
This is a rough formula and I suck at math so I may have written it wrong or there may be a more appropriate way of stating it. Obviously there are many who trade far more frequently, but the formula would still hold the same.