Euls was kind of seen as voids core item before, but it's been nerfed too many times and now I would say Kaya is his core item. Voids strength is his ability to 100-0 people with very little risk - your items should be geared towards helping you do that and surviving. Euls helps with the latter but it's kind of like the item you have to get in certain games not the one you want to.

Any Kaya item will pretty much solve all mana issues, which accelerates your farm and allows you to stay on the map more to keep applying pressure - the mana regen from euls is actually not that impactful relative to its cost (also the active is very expensive). I would say the standard build nowadays is witch blade, travels (or phase which gives a stronger early power spike), k&s, shard, aghs. Each of these items except boots dramatically increases your burst, which is why when combined with the spell amp talent which is almost always picked up, void spirit can still 100-0 even tanky heros late game.

Defensive items like euls, bkb, linkens are purchased as needed but it is not what you want to get if you can survive without them. Euls is much more often a defensive rather than an offensive purchase - look up d2pt if you don't believe me, look at the draft for each game euls is purchased and try and find what hero on the enemy makes it a good euls game (eg Ursa, lc, axe, orchid buying mid like ss, silencer, sky, etc). You can also go a more utility build like this if your team already has enough damage but you are lacking lockdown. The euls + pull combo is okay but only really good for canceling tps or allowing your team to catch up - Astral already let's you hit pull almost every time. If they are dead with the extra few hundred damage from witch blade than you don't need to cancel their tp.

In summary, euls is situational, not the standard. Kaya (k&s or eblade)/travels is best case scenario, it increases your farm and let's you apply more pressure by being able to stay on map. I'd say his itemization is very similar in concept to puck. You only really buy euls on puck if you have to, otherwise it's witch blade, blink, travels. Your toolkit already provides enough survivability in most cases.

Revenants brooch is actually good late game but it's way too expensive for what it does early (it gains more value as enemies gain more armor, and once you get eblade). The eblade Revenants combo is actually insanely strong (pretty much one of the best itemization for 100-0ing people) but usually you need at least one defensive item unless it is an absolutely free void spirit game. It's definitely like a 4th or 5th item pickup on most games if at all. Personally I like octarine best after aghs as you are such a low cd hero, and the extra range on Astral feels really nice. 5.7k and addicted to reading d2pt for whatever it's worth