Respectfully, a lot of this is nonsense. If people using Like instead of Reblog was “killing” the site, the site would just take the Like button away from us. They don’t because this problem is made up.
Speaking as a decade-long tumblr user, people have ALWAYS hit “like” way more often than “reblog.” There was never a remotely even ratio. “Like” has always been used as a lower-key way to communicate to OP that you enjoyed/approve something enough to react, to save a private list of stuff you might want to see again, and/or to add to the visible “nice job” counter for anyone else who happens across the post. Likes are mostly for your own private interaction with the content on this site, not for public consumption/judgment, which is why they were traditionally private and hidden unless someone directly looked through the notes of individual posts. (And use Likes however you want! But it’s just not true that they’ve traditionally been just a reblog support feature. And there’s no basis to accuse people of “killing” tumblr because they’re using the a feature the way it’s always been used.)
“Reblog,” on the other hand, is for content you want to show on your PERSONAL CURATED BLOG which btw is the BASIC CONCEPT of tumblr. A personal blog is outside-facing and has its own personality and themes and vibes much of the time. It doesn’t have to be dictated by any considerations other than “yeah I definitely want this specific thing on this specific collage of stuff I’ve been developing.” Reblogs have always been more selective and, in fact, served an entirely different purpose than Likes.
Does it suck for artists and gifmakers that they work hard and then don’t always get boosted by the entire audience that gave them positive reactions? Of course, and it always has, but individual bloggers still don’t have any obligation to change their curation choices or alter their personal blog to address that. Feel free to keep reminding newbies that there isn’t an algorithm! Maybe people who really love gifs and art want to consider that reblogging is more incentivizing for the artists on here! And maybe they don’t. At the end of the day, it’s not anyone’s responsibility to give anyone else a 1-to-1 like/reblog ratio.
Do not feel guilty about using YOUR OWN BLOG and the features provided to support it any way you want. If Tumblr ettiquette was about “you can’t passively like something without showcasing it and broadcasting it and duplicating it,” then it would hurt tumblr’s value as something different, freer, more private and more indulgent than twitter et al. A huge appeal of this site is to NOT feel like you HAVE to boost content, like Twitter-style performance art.