Yes, this is just a roundabout way to invest into stocks with borrowed money. There is probably an optimal portfolio for this strategy to minimize the risk but then it is no longer the obvious win that so many people think it is.

If we assume 8% returns and you only put 50% in the stock market and your loan costs 2% interest then your total benefit is only 4%. Putting all of it might get you 6% but you are now taking a significant amount of risk.