Basically, your site takes the value and multiplies it by ATH, meaning that any value will be multiplied by a fixed value, adding the second value, and so on?
Your algorithm is as follows:
Result= (Inpout1 * $69,045) + (Inpout2 * ETH ATH) + (Inpout3 * XRP ATH)....
This can be done using Excel, so you will need to add more things to the site.
It is, indeed, a very simple site. But you overestimate potential users if you think that most of them will create an excel in order to calculate that outcome.
I agree that it would be advisable to add more features to the website, but this is how lean projects work: you don't wait until you built a high-end car in order to sell it, you start with a scooter which still works, instead.
So, from that perspective, there is nothing wrong with the project/experiment. In fact, I think that this is a recurrent question between newbies, that a couple of friends of mine asked me in the past: how much would x be worth if it hit an ATH? they didn't even know coinmarketcap lol. So yes, your service makes sense, another thing is how you increase awareness on it so you generate traffic and monetise it (if that's your aim).