his "calculation" is simply wrong, just as devil pointed out. and very misleading. hope no one takes it seriously. Your simple example shows how wrong it is (how can it "minus" the principal repayment ?
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there is no "official" formula for "rental yield". the only "official" one is the gross yield, that is simply gross rental over gross purchase price. This just gives u an idea of the fundamentals. So you can see roughly if the rental supports the purchase price. After that, the actual yield achieved by individual investor depends entirely on his individual situation. (tax status ? various fees ? etc)
For now, clearly prime area pty rentals do not support the price. So they are all gunning for capital gain. Whether this is logical/normal or not is your judgment. You make the call.