Ok so, it is a strange casting choice based on his previous work. However, since I know very little about both Adam Warlock and Will Poulter, I think that it will be fine.

Why?

Look at Chris Pratt's work before he was Peter Quill. The MCU has this strange power to make what it wants out of who they want. As long as they wanted him for the part, I'm sure it will be fine. That's my 2.1 cents on the matter, since you asked 😁