So I haven't watched any of Wootha's gumroad videos but I am intrigued now to see how the photobashing is used, but I cant help you there.
So we are going to stick to your Wootha inspiration as a goal for your piece. Thank you for stating your intention the way you did because it helps us give you a better critique.
To address the pixelization issue. It really depends on which size you are looking at but two things are giving you that effect.
Super sharp and contrasting in value edges like these.
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And Brush texture pattern repetition. Like these.
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Now we will address these momentarily but before we do I would suggest looking at two more things. This is a theory that I wish I had seen a long time ago regarding the creation of a successful piece of work by your very own Wootha.
This one picture in particular I'd like you to look at. In the top middle triangle, I dont know if he forgot to change it or if he left it in there on purpose, but the word composition, is used instead of abstraction which by some can be interpreted as the same thing when you start a piece.
Here is a GIF Wootha provided on how he did some thumbnails, and a video (only found it on facebook when googled)
And if you look through rest of his portfolio you can see that he does this A LOT. Even in this video where he is almost doing the entire piece in 3d, he is working in massive shapes until he gets his preferred abstraction. However, he has portraits, establishing shots, concept art and splash images. No dragons that I could find. But it doesn't mean you cant take these principles he has shown, and apply them to creatures.
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Lets take some time to go over that material.
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The one thing that I see is that not matter what Wootha does digitally he goes out of his way to make things have a painterly feel. In both composition, and brush work in final pieces. He's not here to ask, but that is what I take away from this research.
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Okay. I'm going to look at this like an art director.
First your image is 3.1k wide. I think its wide enough for print or final work size. Think about how you are going to present your pieces to people. Is it on artstation? Is it at a convention on an Ipad or some similar device? Know how you are going to present it and make sure it looks good on those platforms and you should be good. I dont think you have to make it bigger but you can if you want. I don't think that size is what's causing your pixelization effect.
Second. Lets look at your abstraction. I applied a filter - noise - dust and scratches and we can get a squinty eyed view at your piece.
This second look with the more shapes and abstraction addressed two things that were bothering me. The brightness and white of the mouth needed to be brought down so that you didn't have white flattening your image. If the fire is the brightest thing in your frame, it looks bright, don't add white. And the eye. I was confused if it was two eyes. The anatomy of the dragon overall is a little unclear and I really had to stare at it to understand where the wing was so the form of the dragon could use some time.
And looking at this the background has too much detail for the moment in your piece. It's nice to wander around a piece at times but its not strengthening your composition. I might suggest more of a sweeping foggy mountainous landscape like Wootha instead of a dragon just chilling back there. And you can lose the birds.
And for painterly feel I would suggest trying these brushes like these that came up in a google search but not on Wootha's page. They are pretty good abstract mark makers and can lead you to a lot of happy accidents perhaps.
Normally I would do a paint over but I cant hold a candle to Wootha so I hope that this helps you look at your piece a little differently and learn some tricks to apply.
Best of luck. 
