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, ...).

{
    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)
        throw std::runtime_error(
            "importwallet \"filename\"\n"
            "\nImports keys from a wallet dump file (see dumpwallet). Requires a new wallet backup to include imported keys.\n"
            "\nArguments:\n"
            "1. \"filename\"    (string, required) The wallet file\n"
            "\nExamples:\n"
            "\nDump the wallet\n"
            + HelpExampleCli("dumpwallet", "\"test\"") +
            "\nImport the wallet\n"
            + HelpExampleCli("importwallet", "\"test\"") +
            "\nImport using the json rpc call\n"
            + HelpExampleRpc("importwallet", "\"test\"")
        );
    if (fPruneMode)
        throw JSONRPCError(RPC_WALLET_ERROR, "Importing wallets is disabled in pruned mode");
    WalletRescanReserver reserver(pwallet);
    if (!reserver.reserve()) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
    }
    int64_t nTimeBegin = 0;