ROI is definitely more important than win rate in sports betting, but saying that win rate means nothing is just silly since it's an important factor that cannot be ignored based on my knowledge.
Also, he might actually be trying to offer a legit service, but he needs to prove how reliable he truly is to forum members which probably won't happen if you ask me.
Win rate doesn't mean anything... say you bet long short horses at 30-100 odds (there is many people who do this fulltime)
Your win rate could be 4-6% but you would still be a good profitable winning bettor at those odds.
What you mention is correct but @haunebu is not wrong either. Both PnL and Win rate is important on sports betting because it determines how successful and accurate your prediction is.
A gambler might ended up profitable with 4-6% but how can maintain his profitability in the long run since the kind of bet he is using has too much risk involved which means it’s more on relying to luck just to beat the odds.