It really depends on the stage/GTM motion your company is in. You might want to focus on the user if you are really focused on product-led-growth (PLG) and reaching that point of 'activation' - aka the aha moment when a new user gets the value of your product and why they need it. If you have no idea what I'm talking about I'd suggest exploring this article/site from the product-led collective- https://www.productled.org/foundations/product-led-growth-metrics. Other scenarios where you may want to focus on the user is if you're seeing typical product usage metrics declining (DAU, WAU, MAU, time spent, L21+/28 - percent of users are active more than 20 days of the month)
Prioritzing research with buyers may be more helpful if sales if you're exploring a new sales/GTM motion like moving up market to enterprise, or down market to self serve, targeting new buyers outside of your core buyer, landing/expanding, cross-sell etc. It also can make sense to do research almost exclusively with buyers but also sprinkle in some power users who know your product really well and are a big champion of yours.