Set, The Slayer of Kings - Guide (Year 10) (WORK IN PROGRESS FOR 10.5)

Hello! So first, thanks for the comment and I appreciate the kind words!
I do plan on updating this Guide probably tomorrow (or Friday) with different builds, and tips, regarding the current meta.
My problem with Vital Amp and Seqmet's is, as you said, Ultimate reliant. Although, you are right you will be fighting with ultimate, you shouldn't be ultimate reliant. Especially since, even out of ult, your boxing ability is huge. With that being said, that's not the only problem. In the current meta, where Support Auras make backliners SO much harder to kill, you can't waste item slots on items that will only benefit you in certain conditions. Take the build I currently run (And will be put in my guide soon as well). Protector Of The Jungle, Transcendence, Bloodforge, The Crusher, Heartseeker, Magi's Revenge.
With this build I sit on 362 Power, 147 Phys Prots, and 92 Magical prots, without Protector's Passive and without my Sandstorm Proc'd. The beauty in this build is, I have the survivability that is needed for this current burst meta, while also having the damage necessary to run down ADCs/Mages.
So to summarize my thoughts, it's possible and you might even find success with those items, but they currently do not fit it any of the builds I run with Set nor do I find them useful on the God unless you're in Solo lane or going Bruiser. With Set you will lose fights and even waste Kingslayer in a lot of situations, you could rely on waiting for Cooldowns, but that's not always possible. Especially in high level ranked games where they do play around your ultimate. So being able to box without it, in teamfights and 1v1s is crucial in my opinion. (If you want me to go more in-depth on the items, feel free to DM me but that's my thoughts on it just off the top of my head)
Next, comparing your build with the build I mentioned above, you trade off 65 Physical Prots, 28 Magical Prots, 10 lifesteal, and some movement speed (without the other buffs my build has included with magi's and protectors) for 10 more power, 8 more %pen, ruffly 400 more HP, and 10% more CDR. Not including your Seqment's and Vital.
I like the build, you have the damage and it's NOT by any means a BAD build. It's perfectly viable. My only issue, and maybe one you've encountered or not, I don't think you have the survivability if you get focused in a fight.
If the support does his job, you will burn beads pretty fast in a fight and with less prots you'll have a hard time going in on an enemy team with mid to high CC. Speaking with the numbers, you'll kill someone faster but you do DIE faster as well. Look at it this way, if you are focused, targeted with CC you'll have a hard time killing an enemy then surviving, let alone multiple enemies and living without a large lead.
With my build, I'm trading that extra damage you have, for a free beads that'll give me 10% extra damage to an enemy god, plus 20% movement speed for me and my team (mainly my solo laner that should be diving with me), plus Protectors which enables me to play much more aggressively into an enemy comp if we fight in the jungle since my power will increase by 15% (417 total Power) and my prots by 12% (163 Phys prots/ 103 magical) making late game objective play even better. On top of if I kill an enemy, Bloodforge shield and movement speed increases my survivability and kill potential by EVEN MORE.
Like I said, your build is viable and at the end of the day, my arguments are situations in which my build will probably be more efficient that yours. You could most likely make valid counter arguments and at the end of the day it's more personal preference/playstyle.
I will say though, I don't think Bumbas is the way to go, on any gods at the moment, since Protectors, is a much better starter in terms of value.
Feel free to comment again or DM me with more questions, or if you want to continue this discussion as I'm always open to different perspectives etc.
Thank you once again for the comment and the kind words <3

Yea, I can understand the struggle with Set on a game mode like Slash.
So usually, unless I want to go full damage, I'll run a build like Bluestone, Trans, Prophetics, Glad, Stone of Binding, then a filler item but usually heartseeker or Brawlers. With this build, you'll mainly look to fight a lot in the early to mid game, but ALWAYS play around another tank character on your team if you have one, if not you'll get easily focused. Focus on people with no escape, or maybe people who are low. You'll be tanky enough to survive an extended encounter while your ult should be enough to get some kills.
An alternative play style would be a Bluestone full damage build. In that case, you'll essentially just want to poke. Constantly 1 then 2 any Squishies. Then the same tip I gave you for the bruiser build applies here. You'll want to wait for your tanks to go in and grab the damage, then look for solo kills etc. Picking up Blood forge 2nd or 3rd item so you can try and snowball would also be a good idea. Going around trying to find 1v1s for the most part isn't going to work. So when you're full damage, the most you can do is farm and poke. If you catch a lead THEN go for invades to start fights etc. These are just some tips I came up with from the top of my head, but during the weekend I can add a tab dedicated to Slash and other gamemodes.
Hope this helps!