You're incorrect. If you backtest a system and get many years of results it doesn't predict the future but it doesn't mean the live betting will inherently be worse than what you backtested. That's just an assumption, not a fact whatsoever. If you go back long enough you can get an average that the trend will almost always defer to. That's called statistics. Also, just off the top of my head:
Stiflers MLB system performed exactly as backtested
Stiflers NBA system this year is performing WORSE on a Covers backtest than live betting it, the exact opposite of what you said
Wallco's Chase -110 went UNDEFEATED it's first year, that's performing better than any of his backtested years
Stiflers MLB system performed exactly as backtested
Stiflers NBA system this year is performing WORSE on a Covers backtest than live betting it, the exact opposite of what you said
Wallco's Chase -110 went UNDEFEATED it's first year, that's performing better than any of his backtested years