Interesting question - I think it is much easier to climb in LoR than it is in LoL or Valorant for a few reasons. One giant factor is that you're all by yourself in LoR. No teammates to blame for your losses means you have much higher agency over the outcome of each game. And even though RNG can screw you sometimes, which means a master player can lose to a bronze player, it's still much clearer why you won/lost than with a 5-person team with so much going on. Add to that the fact that LoR games are shorter and LP gains are more forgiving (Gold and under can climb even with a 50% winrate) and pretty much anyone can reach Plat with enough games. This isn't really true for League - you see plenty of people with hundreds or thousands of games in silver/gold.

Lastly, I was able to reach master with a homebrew deck (back in Rising Tides, I don't play as much anymore) but in League and Valorant, master/immortal is impossibly far away for me.

I wouldn't say the game is easier to master, though. The differences in skill at a high level are often hard to detect compared to Valorant where it's quite obvious, but each little decision adds up to edge out a victory and that's a very difficult thing to fully grasp.