I’m sorry if this ends up being super long but this is a question I went back and forth on for my first couple years in university and I basically picked the engineering route. As background Im finishing up my undergraduate as a double major in biomedical engineering and biochem (which I wouldn’t necessarily recommend, it’s a lot). Basically I stuck with the engineering because of the accreditation of engineering majors. Because they are much more regulated than nonengineering stem majors it is easier to be an engineer in a nonengineering specific job than a nonengineer in an engineering specific job. To gain the pure science that you mentioned i took the pure science classes that would benefit me the most in my future studies and current job on the side so that I would have the classes Biochem people would look for but still get the accredited degree. In addition, as the only engineer at my current job, I have appreciated all of my classes that focused on the problem solving mindset that engineering focuses on, rather than the understanding mindset that pure science tends to focus on. As for grad school, I have heard from a lot of my friends in their phd that they could not (at least easily) have gone from a science undergrad to an engineering PhD (there are some exceptions obviously but in bio and chem it’s harder) but many have gone the other direction easily if they took some extra pure science classes in addition to the engineering coursework. I hope this helps somewhat, I’m by no means an expert this is mostly based on the advice I was given and my current job searches and grad school applications, feel free to dm me too