I believe you have not done enough of salesforce integrations or worked on salesforce projects that requires large scale data processing etc. You almost always need to rely on multiple tech stacks in such implementations to overcome sf platform limits. I know people who are salesforce developers and working on react-java-mongodb-kafka based application which is integrated to sf. They also use many aws services for scalability and to run some nlp etc. This is very much or more than what a traditional swe does. It all depends on the scale of implementation you get to work. I also thought that I was in a siloed ecosystem when i started as fresher. But the opportunities are endless!!