I don't know how pedantic you're intending to be here; what do you consider a "campaign contribution". If you use the traditional definition of a "campaign contribution", that is, money given to the candidate to be spent on election campaigns, then this is completely false; lobbyists cannot give any more money to campaigns than regular people can.

The power of large lobbies is more closely related to the fact that they represent a large number of constituents who donate and vote (approximately) as a block.

I don't follow. Lobbying is paid for by corporations and organizations. The financial conflicts of interests that this poses on legislators is separate from campaign contributions. For instance, a legislator cannot use the latter for anything but campaign expenses [0]. But a legislator, after leaving office, can go to work for a friendly corporation (though there are laws requiring a "cooling off" period before they can directly lobby Congress).

[0] https://www.washingtonpost.com/politics/mike-pence-used-camp...

When The Young Turks spent millions of dollars in air time endorsing Hillary, was that a campaign contribution?

No, for the same reason that astroturfing online about sending the troops into south side Chicago isn't a campaign contribution; it's not exchanging money for influence.

With your example, Hillary Clinton would be a billionaire for doing that inane dance on Ellen.