How did the primary elections & the 17th amendment move the us from a less democratic to a more democratic system ?

Voters get more control over nomination process, taken away from political parties - mandated direct election of U.S. senators.

Americans did not directly vote for senators for the first 125 years of the Federal Government. The Constitution, as it was adopted in 1788, stated that senators would be elected by state legislatures.

The first proposal to amend the Constitution to elect senators by popular vote was introduced in the U.S. House of Representatives in 1826, but the idea did not gain considerable support until the late 19th century when several problems related to Senate elections had become evident.

The Seventeenth Amendment was ratified in 1913 and provided for the direct election of U.S. senators by citizens. Until 1913 state legislatures had elected U.S. senators.

Ratification of the amendment followed decades of insistence that the power to elect senators should be placed in the hands of ordinary voters. This successful struggle marked a major victory for progressivism—the early twentieth-century political movement dedicated to pushing government at all levels toward reform.

In addition to serving the longer-range goals of the reformers, the campaign on behalf of the amendment sought to end delays and what was widely perceived as corruption in the election of senators by state legislatures.

For further reading, see links below:

www.archives.gov

legal-dictionary.thefreedictionary.com

www.britannica.com