### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current behaviour

See inline discussion at https://github.com/bitcoin/bitcoin/pull/26467#discussion_r1269177446

@whitslack:

> Consider the case where I am paying someone on chain under the stipulation that _they_ will eat the mining fee. (Thus, I specify _their_ address in `subtractfeefrom` when I'm constructing my transaction.) Later, they tell me that they can't wait for confirmation any longer and need an urgent fee bump. If I naïvely specify their output as the `reduce_output`, I may end up paying them _**much more**_ than I intended to if I only have large UTxOs in my wallet.


### Expected behaviour

Not sure.

Improving the docs is one option, but this behaviour seem quite counter intuitive.

My own suggestion:

> Should we disable the adding of new inputs when `reduce_output` is set? If someone really intends to do that, they should probably use `outputs`.

### Steps to reproduce

Haven't tried.

### Relevant log output

_No response_

### How did you obtain Bitcoin Core

Compiled from source

### What version of Bitcoin Core are you using?

Master after #26467

### Operating system and version

Any

### Machine specifications

_No response_
{"changeAddress", RPCArg::Type::STR, RPCArg::DefaultHint{"automatic"}, "The bitcoin address to receive the change"},
                            {"changePosition", RPCArg::Type::NUM, RPCArg::DefaultHint{"random"}, "The index of the change output"},
                            {"change_type", RPCArg::Type::STR, RPCArg::DefaultHint{"set by -changetype"}, "The output type to use. Only valid if changeAddress is not specified. Options are \"legacy\", \"p2sh-segwit\", \"bech32\", and \"bech32m\"."},
                            {"includeWatching", RPCArg::Type::BOOL, RPCArg::DefaultHint{"true for watch-only wallets, otherwise false"}, "Also select inputs which are watch only.\n"
                                                          "Only solvable inputs can be used. Watch-only destinations are solvable if the public key and/or output script was imported,\n"
                                                          "e.g. with 'importpubkey' or 'importmulti' with the 'pubkeys' or 'desc' field."},
                            {"lockUnspents", RPCArg::Type::BOOL, RPCArg::Default{false}, "Lock selected unspent outputs"},
                            {"fee_rate", RPCArg::Type::AMOUNT, RPCArg::DefaultHint{"not set, fall back to wallet fee estimation"}, "Specify a fee rate in " + CURRENCY_ATOM + "/vB."},
                            {"feeRate", RPCArg::Type::AMOUNT, RPCArg::DefaultHint{"not set, fall back to wallet fee estimation"}, "Specify a fee rate in " + CURRENCY_UNIT + "/kvB."},
                            {"subtractFeeFromOutputs", RPCArg::Type::ARR, RPCArg::Default{UniValue::VARR}, "The integers.\n"
                                                          "The fee will be equally deducted from the amount of each specified output.\n"
                                                          "Those recipients will receive less bitcoins than you enter in their corresponding amount field.\n"
                                                          "If no outputs are specified here, the sender pays the fee.",
                                {
                                    {"vout_index", RPCArg::Type::NUM, RPCArg::Optional::OMITTED, "The zero-based output index, before a change output is added."},
                                },
                            },
                            {"input_weights", RPCArg::Type::ARR, RPCArg::Optional::OMITTED, "Inputs and their corresponding weights",
                                {
                                    {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "",
                                        {
                                            {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
                                            {"vout", RPCArg::Type::NUM, RPCArg::Optional::NO, "The output index"},
                                            {"weight", RPCArg::Type::NUM, RPCArg::Optional::NO, "The maximum weight for this input, "
                                                "including the weight of the outpoint and sequence number. "
                                                "Note that serialized signature sizes are not guaranteed to be consistent, "
                                                "so the maximum DER signatures size of 73 bytes should be used when considering ECDSA signatures."
                                                "Remember to convert serialized sizes to weight units when necessary."},
                                        },
                                    },