Fortunately, most accredited registrars that offer reseller programs allow domain registrants to claim back their domains and manage them directly through the registrars. So there's no stuck-with-a-middle-man issue as you described.

IMO the real danger is when the hosting provider is a registrar. Domain registrars have a lot of power, because for most TLDs the registry never touches your personal information - the registrars do. The registrars set the EPP code, which is the key to transfer your domain away. A reseller generally cannot prevent a domain to be transferred away if the registrant insists to (the most a reseller can do is to keep sending locking domain API calls).