I think the main thing you can take from the language/framework descriptions above is that you should outright ignore what people say about tools they don't act

I think the main thing you can take from the language/framework descriptions above is that you should outright ignore what people say about tools they don't actively use. Java and C# absolutely do NOT lack a third-party ecosystem. If anything, both have immensely powerful frameworks behind them and thriving package ecosystems. IMO, your choice only matters if the product you're building is tied to a given library. For example, you might have more luck doing ML in Python/Java than in Ruby, although there is no reason why you can't mix and match depending on what you need to do and what you're trying to accomplish with each.