Replying here since your other comment may be gone. When you phrased it as trees and graphs, it made a lot of since given I looked previously at languages like term-rewriting that did stuff like that. I'll pay you back with one of my most recent finds on handling trees with dedicated language:

https://www.microsoft.com/en-us/research/wp-content/uploads/...

I agree with you on your point that you can mix GC and manual management selectively. As pjmlp, there's quite a few things in between full manual and GC, though, to add to that claim. Ada also has techniques with contracts recently added. Any language with contracts then adds even more if one can express the property in the contract logic for manual or automated methods.

Far as performance, it matters so much that the biggest ecosystems either got there due to better cost/performance ratio or marketing moves by big companies. Those are arguably more important if one wants mass adoption with all the library and funding benefits that come with it. Both Go and Rust are nailing it in their respective niches by balancing performance and safety benefits. Even Haskell developers invested lots of effort into compiler performance with some commercial uptake happening as a result. I tell language authors to ignore performance or ecosystem compatibility at their language's peril.