Yes, it inherently is. Authentication/encryption happens as the very first thing at the network level, before anything resembling a service becomes accessible. This is fundamentally different than for example a web interface, which needs to present "the Web page" to allow the user to log in, which might involve multiple individual parts that can already have a 0-day.
As a more direct comparison: look into historic vulnerabilities between ipsec VPN and SSL VPN. The former is the older technology, the second is more "web like". The number of serious CVEs for the latter over just some manufacturers (Cisco, fortinet, ...) in one year probably beats the number for ipsec in is entire life time.
Going back to Tailscale (or netbird, ...): it is one very secure layer which then secures everything. You can have 1 service or 20, same security. If you expose individual services, c you also expose every possible vulnerability of all of them, so all 20 services if that's what you run.