There are some very definite aspects of Merlin in Gandalph - as there are aspects of Gandalph in modern day 'wise wizard' characters in fiction, such as Dumbeldore in Harry Potter. It's a sort of...recycling thing.

No, but it is just one of those ways in which fiction repeats itself, but not in a bad way, but in the way writers can reflect back on the imaginations of other before them and entwine their own ideas into those of people before.
Tolkien and CS Lewis were good friends - I think I heard someone say before that the first edition of the Hobbit. To say that a character of Gandalph's qualities - loyalty, bravery, humour and, of course, wisdom - was derived from CS Lewis would be a great compliment and a way of expressing his admiration for his fellow writer.
Symestreem, why do you say it is odd that he used Merlin because the tales of King Arthur were French?