Yes, I’d say that in general it’s a bad look.
As a matter of fact, landing page generators in general (whether on different domains or subdomains) are something we’ve started advising against. Especially when it is so easy these days to build lasting, dual-purpose content on the website itself which will help with both organic *and* paid traffic.
We have found that especially for higher-margin products and services, the typical qualified lead will browse multiple pages on the site before making the decision. They’ll want to research, visit your homepage, learn about the company, etc before they either purchase the product or make an inquiry. Landing pages (especially if the template is different than the main site) fracture this experience. They’re often a bit behind the times unless you’re selling a cheap impulse purchase item.
It’s easy to track conversions on your own site, especially using GTM. If you’re selling via an e-com platform like WooCommerce or Shopify, even easier since you can just set up enhanced e-commerce tracking via GA.