His main ET move has a 4-TURN cooldown, and its relic slots are terrible. ML-1 YAMATO also only relies on pure damage (outside of a very weak Burn move,) meaning that it's basically doomed against Tanks with high health.
Secondly, its stats are terrible even for Legendary standards, meaning that it's going to be a miracle if it can outspeed or survive long enough to actually do an attack in high leagues (and by "high leagues," we mean Silver II and up.) Its Power and boring movepool result in it not being able to do much as well. Magnetize Immunity? Really? For reference, Magnetize is just Metal Weakness under a different name, and $P gave up on it after Cyberiel was released. However, there's a reason why it's in tier. In addition, you can also use a 0 CD move to regen 40% of its stamina, meaning that you'll probably never have to recharge. It has some ET moves, allowing it to chain attacks, and its cooldowns are overall low. It's easy to tell that even when it was released, it was marketed especially for beginners. In all seriousness, this guy is another example of Nebotus Syndrome: monsters that look cool but suck. ML-1 YAMATO, the only monster in ML to come with an instruction manual, is a monster because his design looks cool. 2.1 wait why is he in the evil legions again.