I dunno how good Shoma would fair but Spectre has killed his DC ripoff koth shoggoth. That doesn't of course means that it guarantees the win or if Shoma is exactly as powerful as koth, but that should give an idea of how he'd fair against such creatures.
Spectre has more power than Strange.
But, Strange has more tricks up his sleeve, can call upon other Spectre-level beings, spells, tricks, and is probably more flexible than Spectre.
fate once defeated spectre but spectre then raised his power level and defeated fate's source of power nabu so basically if spectre wanted he could kill the vishanti and strange would be virtually powerless
But, we don't know if the same rules apply to the Vishanti.
We don't know where their powers come from. If they are limitless. If they come from another being, or beings higher than themselves. Etc.
We already know that the Spectre is not from the Marvel Universe, so he can't hold any control over their dimensions, or the sources of their power.
He is kinda going to have to fight them "as is".
Fate never beat Spectre, their first meeting in Year One, Fate knew he would die fighting Spectre. He was also shown fighting Nabu at the fall of Saddam and Gammorah and defeating him there. Then finally defeating Nabu again in DOV Special.