My main gripe with the deck is: what do you want in the Lost Zone? The 3 other Relicanths, okay, that makes sense, those are useless. But then what? Then you wasted a couple of turns getting stuff in the Zone while your opponent is building up a Reshiram. You need a lot more in the Zone to KO it, and even trading Lucarios for Reshirams is pretty terrible since you need the Basic, Stage 1 and DCE, while they have energy acceleration and Reshiram's a basic.
It's not the autoloss against Mewgar that concerns me. It's the bad choices you are forced to make (aka drawing early and LZing your own good Pokemon if you want to get big hits in) against decks that have more than 100 HP. And there are just way too many of those.
Oh and you incorrectly use the word underrated. Not a big deal, lots of people do that. But it would be underrated if people thought it was bad while it was actually not bad. Currently, people think it's bad and it is in fact bad (since it's not winning anything).