Less true than you think. A lot of the progress in the last year has been tightening agentic prompts/tools and getting out of the way so the model can flex. Subagents/MCP/Skills are all pretty mid, and while there has been some context pruning optimization to avoid carrying tool output along forever, that's mainly a benefit to long running agents and for short tasks you won't notice.

All of these things you mentioned are put into a footnote of the article.