This is not accurate. What MuSig is is an algorithm to construct a multisig Taproot address from multiple public keys securely, and which only requires one (aggregated) signature to spend. So such an output is identical to a singlesig Taproot address.

What you were thinking of was likely Cross-Input Signature Aggregation, which allows you to provide only one signature for all of your inputs. Unfortunately, this is not implemented in Bitcoin yet because it would most probably require a soft-fork (which would come with its own tradeoffs).

Hypothetically if such a feature came to Bitcoin, then large coinjoins would be around 15% cheaper than they are currently. Thus the incentives for batching transactions would be much stronger.