MI200, MI250, and MI300 should work for training. They don't have an exact equivalent to the 4090 but that may be setting the bar too high. Nobody can deliver everything that Nvidia has but better.
It will be harder for a small academic lab to afford MI300, whereas everyone can purchase a few cards costing $1500. And even if I had money to buy MI300, I wouldn't - it is a too risky investment, because we have no idea how suitable they are for common AI research workflows. They need to lower the entry bar, so that people can try out their hardware. Even 80% of the performance of 4090 would be enough at an appropriate price point.