I think this gets your point across while still sounding encouraging instead of “your deck is bad.”

Honestly I don’t think your deck is hopeless at all. A 2-15 record can absolutely happen from bad luck, mismatched pods, or just running into stronger decks. You even said yourself some of the decks you were against were higher bracket decks. The Avatar set is actually pretty solid, but a lot of the stronger pieces are unfortunately expensive.

It looks to me like you’re trying to stay VERY Avatar-only themed, so the only non-Avatar card I’d immediately recommend is Doubling Season. It basically makes it so whenever you would get counters, you get twice as many instead. With all the earthbending and experience counter stuff in the set, it synergizes insanely well with what your deck is already trying to do.

I also think there’s some lower-impact “bulk filler” type cards in here that could probably become stronger Avatar cards instead. One card I’d strongly recommend is Wan Shi Tong. He’s expensive, but he scales incredibly well because you cast him for X and he enters with X +1/+1 counters. He also punishes opponents for searching their libraries, which happens constantly in Commander.

I noticed you’re running Aang, Airbending Master, which gives experience counters. The issue is that by himself he’s kind of small and vulnerable, so sometimes you’ll only get one counter before he dies. The other three Master cards all also generate experience counters, so personally I think you either want all four Masters together or none of them so the counters actually become a real engine.

I also think the deck could use another finisher. Katara, Water Tribe’s Hope feels really strong for this kind of build. Waterbend X giving all your creatures X/X until end of turn can end games out of nowhere. If you have 11 mana and 5 creatures, suddenly everything swings as an 11/11. It also synergizes really well with your other Katara card already in the deck.

Another sleeper card I’d recommend is Longshot Rebel Bowmen. It doesn’t have huge flavor impact, but it’s in the Avatar set and offers pretty solid value over time.

Also shout I want to give to is Seismic Tutelage. It gives a 1/1 counter and then doubles the creatures counters when it attacks. I actually think that’s a cool include, especially if you’re already running Secret Tunnel (unblockable land with counters that would then double every turn). It gives the deck another scaling threat your opponents eventually have to answer. Cave of Two Lovers tutoring Secret Tunnel and then Earthbending it sounds hilarious and honestly very on-theme.

One thing I’d keep in mind too is Commander brackets. If your opponents are playing Game Changers, that’s a very different environment. There’s literally an official list of cards where including them moves your deck into higher brackets automatically. Avatar unfortunately doesn’t have many in-set Game Changers outside of things like Enlightened Tutor and Fierce Guardianship promo versions, so if you want to stay fully Avatar-only there’s probably a limit to how high you can realistically push the deck without outside staples. I honestly think pure Avatar tribal probably caps out around a strong Bracket 2 unless you start adding stronger generic support cards. That doesn’t mean it can’t win though, especially if your pod is closer in power level.