Are Republicans responsible for Democrats trying to pack the Supreme Court given how they handled Garland's and Barrett's nominations?

At least Nancy Pelosi is smart enough to not go ahead with this. She doesn't want to allow Republicans to re-pack the courts in a few years. 

The Kavanaugh sham investigation comes to mind.

There was not a damn thing wrong with the Amy Coney Barrett appointment. 

I will grant you though that not letting the Garland nomination come up for a vote was dirty pool.

But Dems already got their payback on that one by trying to destroy Justice Kavanaugh at his confirmation hearing with the fake sexual assault accusations.

UPDATE McConnell had publicly refined that belief early on in the Trump administration that the nomination should be put on hold when in an election year AND there was split government where 1 party has the Presidency and the other the Senate.  And in fact, the GOP control of the Senate expanded in the 2018 mid-term.
https://news.yahoo.com/mcconnell-republicans-fill-another-supreme-171700577.html

ironically, your entire question revolves around precedents set when democrats controlled congress....

the left are the ones who brought up the subject (and eliminating the Senate filibuster) and the only ones who are touting it now. it guarantees no Republican will ever win an office or introduce another Constitutional bill again. 

Nothing different then what we have done in the past. The reaction, the media , the elected leadership on the left is all that is different. The left continually alters/changes thing when they are in power. Eventually those things are used agaisnt them when they lose power, then they cry about it, it's not fair.