### 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_
{
    if (options.exists("input_weights")) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Input weights should be specified in inputs rather than in options.");
    }
    if (inputs.size() == 0) {
        return;
    }
    UniValue weights(UniValue::VARR);
    for (const UniValue& input : inputs.getValues()) {
        if (input.exists("weight")) {
            weights.push_back(input);
        }
    }
    options.pushKV("input_weights", weights);
}
RPCHelpMan fundrawtransaction()