Bitcoin will always be the number one crypto in coinmarketcap or in any crypto ranking site.
I see no evidence of that. It is entirely possible that your forecast will be right but it is equally plausible that another innovation will over take Bitcoin or that it will be forked again and another battle such as the BTC/BCH will happen and on that occasion divide the community like never before.
Dominance by Bitcoin will probably not last forever but it will probably be dominating for a long time to come.