I cannot really speak for the Crimean War, but I would like to add a general word of caution when studying military history: "Decisive Battles" and Singular Turning points are really big, sexy things to look at and talk about when discussing history, however they are often also a very bad way of looking at things - especially as you transition more and more towards modern history where wars became increasingly complicated. They are look very simple and easy to understand, and in large part that is because they oversimplify matters to facilitate that, which, of course, often leads to misunderstandings as you end trading historical accuracy and nuance for "clarity".

The Crimean War (as well as the American Civil War, the Prussian Wars of the 19th century, the Russo-Japanese War, and a handful of other conflicts) is in large part interesting because it lies in the middle of a transitionary period towards the "modern war" that we would see in World War I and beyond and the post-Napoleonic style of war that swept over "Europe"...well, after Napoleon. Wars, especially modern ones - but by no means only modern ones, as this can also be said of innumerable wars in the pre-modern period - are relatively seldomly decided by single battles, but by entire campaigns and operations. A single war can have multiple "decisive battles" where the "victor" of those decisive battles ends up losing the war at large to the side that won fewer, or even no, "decisive battles". This is because war is extremely complex and extends beyond just battles - which, again, is increasingly true and important as you transition towards the modern period.

As such, I often find questions like "What was the decisive battle of War X?" or "What was the turning point of War Y?" to be interesting technical questions for debate, but of comparatively little value in understanding the war at large and why it unfolded as it did. It's also a big pitfall, as it can make you look for something that doesn't exist, or make you over-emphasize the importance of something that, in reality, had far less value than it is being propped up as having.