Some comments from @sipa in #12702.

___

Yes, I think `importmulti` is superior in every way, except:
* Slightly less convenient to use (it requires redundant information, as you have to explicitly state what you want to import, and then give the keys/... to enable that).
* ~Doesn't support P2SH-P2WPKH yet~. Added in #14454

The latter can be fixed by just adding support for that case. The former can be improved by adding 'default' cases (e.g. if you prove a WIF private key, it can permit omitting the address, ...).

if (pos >= int(tx.vout.size()))
            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid parameter, position too large: %d", pos));
        setSubtractFeeFromOutputs.insert(pos);
    }
    std::string strFailReason;
    if (!pwallet->FundTransaction(tx, fee_out, change_position, strFailReason, lockUnspents, setSubtractFeeFromOutputs, coinControl)) {
        throw JSONRPCError(RPC_WALLET_ERROR, strFailReason);
    }
}
static UniValue fundrawtransaction(const JSONRPCRequest& request)
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 3)
        throw std::runtime_error(
                            "fundrawtransaction \"hexstring\" ( options iswitness )\n"
                            "\nAdd inputs to a transaction until it has enough in value to meet its out value.\n"
                            "This will not modify existing inputs, and will add at most one change output to the outputs.\n"
                            "No existing outputs will be modified unless \"subtractFeeFromOutputs\" is specified.\n"
                            "Note that inputs which were signed may need to be resigned after completion since in/outputs have been added.\n"
                            "The inputs added will not be signed, use signrawtransaction for that.\n"
                            "Note that all existing inputs must have their previous output transaction be in the wallet.\n"
                            "Note that all inputs selected must be of standard form and P2SH scripts must be\n"
                            "in the wallet using importaddress or addmultisigaddress (to calculate fees).\n"
                            "You can see whether this is the case by checking the \"solvable\" field in the listunspent output.\n"
                            "Only pay-to-pubkey, multisig, and P2SH versions thereof are currently supported for watch-only\n"
                            "\nArguments:\n"