Yo! Former Ponza player here. I know there aren't many of us on Tappedout (and the internet period) so I'll try to be of assistance.

I don't know if you look at any newer lists but a lot of them are running Karn, the Great Creator along with Mycosynth Lattice /an artifact package in the sideboard. To my knowledge it gives the deck a lot of flexibility it didn't already have before and might be an answer to some of your sideboard questions.

Here's a list if you're interested in what I'm talking about: https://www.mtggoldfish.com/archetype/modern-gruul-karn#paper

In my opinion, you need some number of Abrade in the main. You'd be surprised how many Modern decks these days run artifacts, and the ones that don't usually have creatures that can be sniped down with it. Speaking of artifacts, Pillage was recently printed in Modern Horizons, so you could probably replace Bramblecrush and maybe 1 Boom / Bust with those. I remember hearing all the Ponza guys raving about it when it was printed, so it's got to be good, right?

Hey I play tons of Ponza and have done for years. I play mostly on MTGO so you local meta might be different if you play at a store, but here is my take on the cards. I think I wrote a smaller book of a comment sorry about that.

first off Inferno Titan!, turn 2 moss into turn 3 titan is the most powerful thing ponza can do. Remember he can be pumped with his ability and often swing for 12 or more damage (when targeting face with the ability) plus he shoots stuff down planeswalkers and creatures alike both when he is played, but also when he attacks. The absolute best finisher for the deck.

I love Bonfire of the Damned and have played with everything from 1 to 4 copies in my main board, the one sided board clear feels so good, but I have come to realise it is just too conditional. It is too reliant on the miracle, i kept telling myself it wasn't but it really is, 7 mana for 3 damage is not worth it, you are already dead to aggro and if you have enough mana to shoot someone down with a big spike you should have already have won. Anger of the Gods in the sideboard are just better wipeing you own dudes does not really matter if the opponent just loses to a wipe and the exile of creatures is so important vs graveyard stuff.

You play Boom / Bust which i have experimented with as well, you say it cost less than Pillage, this is not true as you need 2 mana and a untapped fetch in order to play it, so that is 3 mana, plus you need a fetch to play it that is super conditional even with 8 fetches. And depending on Bust part to win the game is not something you should never wish to happen.

Artifacts, one thing Ponza loses to is Aether Vial, all the land disruption does nothing against it. So in order not to lose to that i suggest to main board Pillage or Abrade they are so good with the flexibility doing what the deck is already trying to do and able to remove artifacts when needed is super useful. Other cards they help against is Cranial Plating in affinity, Oblivion Stone the only answer tron really has and Arcum's Astrolabe which bypasses all moon activity and of course all the stupid artifact creatures that randomly appear like Walking Ballista and Myr Superion.

I know you play Primal Command for all the artifacts and such nonsense, I have played it myself in the past, but for 5 mana it is really slow and to that it is also quite conditional on its effectiveness some games it can just outright win it like mill or somthing, but more often you will lose with it in hand and it is the worst. searching for a big guy to finish with is not much good either as you would much rather play the big guy insteal of the command and i have so often lost with the searched up guy in hand as the opponent will know to kill off your mana dorks or keep a counter in hand because you revealed your plan.

your Eternal Witness Stampeding Serow combo is cute, but playing cards that are not just good on their own are a big mistake, blue deck might get away with it, but green really relies upoun mana effectiveness. I see how you can use witness's with other cards in your deck and be able to slowly grind value out, but in reality something like Tireless Tracker would be much better as it just gives value by existing and can end the game.

Okay how to win vs the bad matcups like burn, storm and control. It is so hard to win vs storm, you already use Scavenging Ooze, but other cards i use on and off is Cindervines, Weather the Storm and Damping Sphere.

to win against burn the most effective strategy I have used is the Madcap Experiment and Platinum Emperion combo. otherwise Obstinate Baloth and Kitchen Finks works, the baloth having added bonus of being really good against Burning Inquiry and Liliana of the Veil.

lastly control, i absolutely hate control. oh well here the best thing is getting a Blood Moon out turn 2 it is so important that running stuff like Magus of the Moon is very much worth it. otherwise there is of course Thrun, the Last Troll and Choke.

Hope i helped you out in some way and not just made you angry or something.

Does Noxious Revival have a place in this deck, either to hold off a land draw or to get back one of the beat down critters?