It is not the creator of all Pokemon. Arceus created the first Pokemon and as a result possible also Mew. Mew is like Adam and Eve in one as it is the ancestor of all Pokemon. So all Pokemon came out of it's DNA, however the "god " of Pokemon is most Likely Arceus seeing as he is the creator deity.
The reason it can learn all moves barring some is that all was given to him, but that doesn't necessarily mean he is the most powerful and is by far not powerful enough to be the "gd" Pokemon (inb4 Mew bans me :P). It is surpassed in power by many others, however it's ability to transform into anything it desires is quite impressive. It is quite logic that Arceus is the "god" of Pokemon seeing as it could battle Dialga, Palkia and Giratina without receiving a scratch in a 3 vs 1 battle and those 3 are known to be exceptionally powerful Pokemon