Should the Black Templars have been one of the original legions?

Sometimes I wonder if it would have been a good idea for the Templars to be one of the original legions. When I think about it, I think they would have been an excellent legion, although I also notice a potential problem: in the 30,000th millennium, they might have felt somewhat repetitive. This is because the Templars are, at their core, fanatical knights who worship the Emperor as a god, a concept very similar to that of the Dark Angels, which could make them feel redundant. However, beyond that, I don't think they're that similar, as the Dark Angels were more focused on specialized missions and had a more orderly structure, while the Templars are characterized by their brutality and lack of complex strategies in exchange for the ability to better serve as a front line of attack.

That's why I think the Templars would have fit quite well as a legion rather than just a chapter. Furthermore, their devotion to the Emperor would make more sense, as they would have had the opportunity to see him in his full glory. Furthermore, their existence as a legion could have filled one of the two gaps left by the lost legions.