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(
            "dumpprivkey \"address\"\n"
            "\nReveals the private key corresponding to 'address'.\n"
            "Then the importprivkey can be used with this output\n"
            "\nArguments:\n"
            "1. \"address\"   (string, required) The bitcoin address for the private key\n"
            "\nResult:\n"
            "\"key\"                (string) The private key\n"
            "\nExamples:\n"
            + HelpExampleCli("dumpprivkey", "\"myaddress\"")
            + HelpExampleCli("importprivkey", "\"mykey\"")
            + HelpExampleRpc("dumpprivkey", "\"myaddress\"")
        );