There are certainly quirks, but identifying and conforming to those quirks is not that complex. E.g. I had Kimi "fix" my harness to work better with Kimi by pointing it at the (open source) kimi-cli + web search and telling it to figure out which differences might matter (it made compaction more aggressive, and worked around some known looping issues (by triggering compaction if it spotted looping tool calls). Largely addressing the quirks tend to harden the harness for other models too. But, yeah, it is more work to make the smaller models work with instead of against the harness.