well, it depends on what you mean by that. You can have two plugins that have the same algorithm, but with different settings and in a different package do wildly different things. Technically, a synth is just some tone generators and filters and such, but the way it’s packaged makes a huge difference in what can be done with it. A house is just studs, copper wire and some drywall, but the way in which it’s packaged can make a pretty big difference.
In the same sense, you can have a good song or a lame song with the same chord progression.
When making a plugin, the algorithm is usually the easiest part (big stress on the word ‘usually’). The hardest part of making a plugin is packaging it up in a way that people can make use of it. I’d say that, depending on the plugin, may 5% of the time is spent making new algorithms, and 95% of the time is spent trying to make it usable.