CA - My rough build/rent projections look accurate? 2 SF + 2 ADU

[Rami W.]

El Cajon, CA. 1 acre (rs-20) flat buildable lot owned free and clear with utilities. Will split lot (sb9?) and build 2 SF + 2 ADUs. Goal is to build and rent. 

These numbers seem LOW to me. Is this fair or am I off? The ADU's have okay ROI, but the larger unit seems quite low at 2.5% RoC. I'd expect a better return since the lot is owned free and clear so not sure what I am doing wrong here. Any advice? Thanks!