Organic traffic analyst, 10+ years of extensive web marketing experience. My main porpouse is to increase website traffic, mensure website metrics and boost organic traffic sales.
Metrics that you are analyzing are percentage, It means if integers values decreased probably percentages will increase. So, you need to understand what are website long-terms top ranking. If you provided information contents without a call-to-action or your blog user experience is no good, probably your blog wil keep a low performance.
Best choice is create a subdomain, because each trainer Will have a different content and layout. But for Google each subdomain is a new website, no share relevance between them. If you can use a page model for each trainer, you can use directory structure such as domain.com/trainers/name, so you will distribue link juice across pages, improving website architecture.