Leo was past his prime, and he tried his best to fight it with daily training, but there was a limit to what he could do.
Vampires had an advantage in this, their body structures were different, and Leo was liking it. ( Online novel: My vampire system)
Is that simply a variant of the simple past tense with the same meaning?
Leo liked it.
From what I have learned, static verbs are not in harmony with progressive. Maybe online novels don't follow strict grammar rules？
While it's true that state verbs don't play well with the continuous aspect, there's a modern (last 20 years or so) trend towards using state verbs with continuous and slightly altering the meaning.
State verbs like "like/love" in the continuous roughly mean, "enjoying" or "appreciating".
You may have seen the McDonald's slogan, "I'm lovin' it". It means the same thing.
So in your example there, the writer isn't telling you Leo's thoughts or opinion on vampire body structures, but that in that moment he was enjoying the different body structure.
Another modern example is "understand", which was normally a state verb can now be used with continuous, usually in a question or negative:
I don't think you're quite understanding me.
Not all state verbs can do this. Some, like "know", have resisted this change:
I'm knowing what you mean
