Duplicating pages to better target the title for keywords is not an effective SEO strategy. There are two things that will work against you:
- Google detects when pages are substantially duplicate and chooses just one of them to index. If you have three pages that only differ in their title, only one of them has a chance of getting indexed.
- Google see such practices as spammy and may penalize sites that duplicate pages for keyword optimization purposes.
Instead it is better to use all the keywords in a single page as you have been doing.
References:
Doorway pages - Search Console Help
Doorways are sites or pages created to rank highly for specific search queries. They are bad for users because they can lead to multiple similar pages in user search results, where each result ends up taking the user to essentially the same destination.
What is duplicate content and how can I avoid being penalized for it on my site?