LLMs (and probably most NNs) have lots of meaningfull, interpretable linear feature directions. These can be found though various unsupervised methods (e.g. SAEs) and supervised methods (e.g. linear probs).
However, most human interpretable features, are not what I would call the models true features.
If you find the true features, the network should look sparse and modular, up to noise factors. If you find the true network decomposition, than removing the what's left over should imporve performance, not make it wors.
Because the network has a limited number of orthogonal directions, there will be interference terms that the network would like to remove, but can't. A real network decomposition will be everything except this noise.
This is what I think mech-interp should be looking for
It's possible that I'm wrong and there is no such thing as "the networks true features". But we've (humans colectivly) only just started this reaserch agenda. The fact that we haven't found it yet, is not much evidence either way.
You might want to look at "Jacobian Sparse Autoencoders: Sparsify Computations, Not Just Activations" — they're trying to optimize for what you describe, and apparently had some success. Crosscoders are another attempt.
2Linda Linsefors
I do exect some amount of superpossition, i.e. the model is using almost orthogonal directions to encode more concept than it has neurons. Depending on what you mean by "larger" this will result in a world model that is larger than the network. However such an encoding will also result in noise. Superpossition will nessesarely lead to unwanted small amplitude connections between uncorelated concepts. Removing these should imporve performance, and if it dosn't it means that you did the decomposition wrong.