Sure, transactions are pairs (or balanced sets) of entries. Entries however, are exactly plus/minus movements along a single line in a single account. Sign (+/-) reflects that much better than debit/credit labeling does.
> There's always a tendency to simplify the model and elminate the balancing interaction and check.
Using +/- in place of credit/debit does not eliminate the balancing interaction. In fact, it makes exactly what is done in the balancing interaction more explicit.
> You're making a choice to use plus/minus for credit/debit is one of the distinctions, you could just have easily use it for asset/liability or income/expense. Why favor credit/debit?
Because income, expense, asset, and liability, are all kinds of accounts, and credit and debit are not, they are descriptors of whether an entry (or balance) is a flow (or accumulation of flow) of value into (debit) or out of (credit) an account.