One can use all the sites mentioned without giving out one's login credentials for one's accounts. One simply updates the total number of shares in the external accounts manually.
One doesn't have to put any transactions in these sites, just the total number of shares whenever they change significantly. All the sites will look up prices for you. I've used Fidelity, Vanguard, Morningstar, Personal Capital, and TDAmeritrade which all have places to enter manually portfolios.
Let's face it, one should not have a lot of transactions and the total number of shares for any investment in any account should not change most of the time. Furthermore, one should not have a lot of different investments in each account. Indeed, I think one should probably have no more then one or two investments in each account. For instance, a Roth IRA could have one single fund in it.
Furthermore, one should login online anyways to each of their accounts at least once a month to check for fraud and hacking. Once a month is about the most one needs to see any changes in number of shares.
If you have a Windows PC, Microsoft has free software called MS Money that is freely downloadable and can keep track of all your numbers without an internet connection and without logging in to your accounts. You would have to enter the numbers manually, but I think that is a good thing since it will help nudge you to have fewer investments and make fewer transactions. This would get one all the historical trends and graphs and charts, too.
The OP writes they let things sit for a long term, so I recommend they check out the Fidelity Guided Portfolio Summary (GPS) tool which can be found under the "Analysis" tab of their Fidelity account as shown next: