That’s seems an off-axis question to me. “These devs are expensive and a constraint on our growth. I want to hear more tappy-tappy…”
What’s the alternative if you have a good backend programmer and an excess of front-end work at the moment? Have the backend plow further ahead? Move items that “belong” in the front-end to the backend just for dev capacity reasons? Decide your architecture based on which devs are free in a given sprint?
That backend dev might be 50% as efficient and still result in more total value delivered.