It's just accounts with level 1 cards playing against other accounts with level 1 cards over and over and slowly but surely moving up the leagues.

Then the point system is borked.

If a League of Legends player with a "true" ability of Silver 1 is on Silver 1, he can play literally unlimited matches but he will stay at Silver 1, as he'll win 50% of the matches and lose 50% of the matches. Small swings obviously happens, but this hypotetical player will end up in the same place as his teoretical, true ability. That's what a MMR system is meant to do.

If in Splinterlands, bot accounts full of lvl 1 cards can just climb through the leagues by beating other bot accounts running the same bot software, something's not right. If they're at the same ability level (eg same bot software) and using the same (or really similar) cards, they should just keep wasting their time against each other, without climbing the leagues.

Back to the LoL example: if you take 1000 "true" Silver 1 players and put them against each other, after thousands of matches they'll all still be at Silver 1, as that's their correct ranking. They can't climb if they're not actually playing better.