That's fair. And I'm not arguing that YAML anchors can never be a problem. I am saying that layering in a whole custom build system to handle a 250 line ci.yml file is not the trade-off I'd make. What I'd hazard to say most teams do in that situation is duplicate config, which is not without its own problems. I think YAML anchors is a fine solution for these cases and don't think they'll lead to total chaos. Alas, not all config options can be hoisted to a higher level and I'm trusting a team has explored that option when it's available.

If you're dealing with 10s of files that are 1000s of lines long, then YAML anchors may very well not be the ideal option. Having the choice lets each team find what works best for them.