First comment, not on essence: the difference between your starter and pro plan is $5. If people have fewer than 85k runs / month, you're asking them to commit to $500/mo spend to get longer retention. That's... fine, but you can probably charge more for that. For people with more than 85k runs / month, you're only charging them $5/mo for that retention - and making the pricing page more complicated.
One option: Increase your base price from $40 to $45, and say longer retention is only available for customers paying >$500/mo. You'll get what you have today but simpler.
Another option: Charge more for longer retention! $10/1k-runs makes sense, or even $15. If retention is the differentiation between the two plans, charge for it like it's worth being an upsell.