You need both Product Developers and Infrastructure Developers but the balance depends on understanding the difference between laundromats and startups.
If you want to start a laundromat you can copy existing laundromats and it will probably work out fine. It's not mysterious why customers give laundromats their hard-earned quarters. Or I guess it's probably Apple Pay or something now. Who knows? I'm old and don't go to laundromats.
If you were good at school you would be great at running a laundromat. You figure out the playbook: sit quietly, pay attention, take notes, follow directions and deal with the excruciating boredom in a way that's acceptable to society. Then you execute the playbook and reap the rewards: Gold stars on the fridge! Running a laundromat, just like succeeding at school, requires self-discipline, hard work and a pre-frontal cortex that isn't riddled with ADHD — but there is little risk in the outcome.
Startups have no playbook. Instead, there is a search space and your job is to run an algorithm to find a business. Your success depends on how close you were to the answer to begin with, the quality of your search algorithm and how much time you have to make guesses multiplied by how fast you can learn you were wrong. Hard work and self-discipline are still required but ADHD brains are welcome here! Outcomes are not guaranteed. You're failing until you're not.
If your business is established at all then parts of it look like a laundromat and other bits look like a startup.