I don't like heavy cropping in post. I try and compose the framing I want, but in this instance, the lens just wasn't up to it. So, we get lots of water lettuce :)
I split my subjects into wildlife and others: for the "Others", Landscape, say, its perfectly correct to want to take the photo and "Fill the frame", only cropping if you need to straighten the shot or there's an actively irritating out of focus thing at one edge. You move, select the right lens, zoom, etc. to achieve that, before you press the shutter.
With wildlife, I take what I can, and fully expect to crop, even down to a tenth of the area of the original shot. That's because I don't have the luxury to get closer or change lens, or indeed do much to play with camera settings - if I do, the bird or animal will likely flee (or just move because it wants to). My only acknowledgement of "Fill the frame" is that after taking the best shot I can at the point of first spotting the subject, I will then try and get closer, just in case I get lucky.
But, it's your photo and so your choice - if it doesn't satisfy you, it's a failure, regardless of the opinion of others.