4 leads with 11 people might be too much. You only have to change things a little bit at a time. Maybe turn 3 or 4 of your employees into a group reporting to one lead, and see how that works out.

Don't be afraid to make your best developers into leads. If you think they would be the best leads, do it. You will lose direct contribution, but you need to make this decision for the long term. You want an atmosphere of performance being rewarded, rather than promoting long-time less-competent people. Your other employees will see what you do.