Correct me if I'm wrong. But the body of water at Puteri Harbour we see is not, strictly speaking, sea but just a "straits"? I've been there twice. It's psychologically nicer than other places just because there is water. But I have to say the water isn't the nice blue type and not a sea as many often describe it as. The nice pictures with deep blue skies and water we see in advertisements are just artist's impressions. The real stuff isn't as great.
Anyway, there's already a price to pay for it. Puteri Harbour costs a lot more than other residential condos. So your upfront investment is already higher.
As for comparison of Puteri Harbour to Sentosa, I wouldn't think about that. Yes. it feels that way. You can think of it as the closest you can get to something like Sentosa. The experience is different though. Sentosa is well-established and vibrant. The only thing you get is it's cheaper on your wallet when you buy Puteri Harbour. But it's incorrect to attach to Puteri Harbour the same value as a upmarket seafront residential place like Sentosa.
It's like comparing an Apple iPhone to Xiaomi. Some people tell me Xiaomi is value for money. It has many functions you can find in iPhone for a much lower price. But you will realize the experience of using an iPhone is so much different. Value-wise, an iPhone is much sought after. A Xiami, well... it has little or no resale value. That's how it is: Apple iPhone (Sentosa) and Xiaomi (Puteri Harbour).
Rental wise, I'm not sure. You bought it at high price in Puteri Harbour, the developer has already passed on the cost to you. It's not as if Puteri Harbour existed in 2010 and you bought it for S$100k. You already bought it at such a high price (by JB standard). From a rental point of view and future selling, it is a lot more difficult for you to recoup your $$. Not forgetting the oversupply. Go check out how Imepria is doing now. It's very disappointing. Find out also how much the owners have lost based on the depreciating currency exchange.
I'm not saying Puteri Harbour is not good. It's good but only for your own occupancy. And you must have the cash to throw. Like buying a car.
If you are thinking of making good $$ from your property there, think carefully again. I find some here imagine a lot, like when they say: "In 5 years time, we will have this and that coming up. How vibrant it will be.... I can buy a yacht and travel from PH to SG, my property will rise in value, etc".
Do understand you are still buying a JB property. It's not so simple to say if there is a business planned in a certain location = your property will boom. There are a lot other factors to consider.
Buy if you have excess cash to splurge. Don't buy cos you think it's the next Sentosa. Your risk and disappointment will be high.