I have been toying with a mono white belcher as well and mine is a lot more all in than yours. Pure belcher is the name if you wanted to check it out (it is a very outdated list though). My only real concern about your list is the reliance of endless horizons to pull most of your lands out. But then again, maybe the creature suite can make up for that. Let me know how it performs.

So, I've been trying to build a Mono-White Belcher since, I don't know... 2017 maybe... and the very first build I tried was an all-in consistency-based deck. It was too fragile.

Now the deck has been doing pretty nicely since I no longer rely on only one plan. Now I have more ways to deal and interact with the board and apply pressure even without the belcher plan.

The reason for the switch was:

1. The belcher combo is kind of slow even if we use Simian Spirit Guides. One of the fastes ways to combo is turn-3 horizons/belcher -> turn-4 the other combo pice -> turn-5 activate belcher. That leaves a huge window for interaction.

2. Thinking about that, if we hold off the combo to minimize the vulnerability window, we get a turn-5 horizon -> turn 6 belcher+activation. That is still kind of slow.

So, if we abandon the "Pure Belcher" plan, we get to deal with potential threats the opponent might have. And, since we run 4 copies of horizon and 4 copies of belcher, we are bound to eventually draw the combo. So, we'll either win by control+beatdown or by comboing and (in some cases) steal the win from unaware opponents.

I cannot vouch entirely for the quality of the players I face in MTGO. But all this testing I did before switching to MTGO and all these notes I took from previous versions of the deck were made in my LGS. But my LGS is the one I can vouch for when it comes about player quality since it is a gathering point of some of the few high-level judges and pro players in my country, so that accounts for something, for sure (it is pretty much as competitive of a meta as it can get and it is likely one of the most competitive metas in my country).

After I repeatedly tested against quite a lot of tiered decks, since my LGS meta rarely, very rarely, has rogue/budget decks, I retreated and abandoned the idea for a while.

Then, it came to me out of the blue. And now it is as you see it now. And, I have to say... It is pretty much the best version I've played since I started this journey.

Also, another Edit. The results I've been having are much better to the ones I had in previous versions. Perhaps that's partly due to the meta shift from a couple years, but that is probably also partly due to the new board presence creatures added in this version.

I see you have 4x Batterskull, so have you considered running a playset of Stoneforge Mystics? Also, in addition to 4x Path to Exile and 3x Wrath of God, Porphyry Nodes is really cheap and can definitely gum up the board a lot. In any mono white controlish deck, I like to run nodes and a bunch of wrath effects since it slows the game down to a snail's pace.

Well not really gum up the board but like screw with it if you know what I mean lol

Thanks for the suggestions, zapyourtumor, but, after thinking about them for a while, I don't quite feel that's what I how I want to play the deck. Atm I don't feel the need to tutor Batterskull since the chances of naturally drawing it are high (and stoneforge would demand some slots that can be filled with yet-to-discover-options) and Porphiry Nodes I don't really see it fitting well...

Well the point of having the Stoneforge Mystics is so you can cut down to a singleton of Batterskull, and then you can add a few other equipments like the swords if you want. Although I understand if you don't want to make the deck too stoneblade-y