It might be because the V cards look tacky with it
If you play into the synergy and run a load of powerful artifact creatures in this deck, you can all but ignore Toph's secondary effect and just use it as an extra insurance policy for your most valuable artifacts
Getting a $5 Huatli, the Sun's Heart isn't going to make an otherwise not-worthwhile Secret Lair drop worth buying, while getting a $100 Liliana, Dreadhorde General would make even the least valuable Secret Lair a win
What is actually the most significant thing about Prime Time is that once he has resolved you are there so to speak
Instead of having lots of hoops to jump through to make Angels, all you need to do here is put an artifact into play
As for the X spells themselves, that includes a rich variety of Hydras such as Hydroid Krasis, which is overwhelmingly strong even without Zaxara there to generate additional value on the side, along with other staple Hydras like Lifeblood Hydra, Protean Hydra, and the mighty Genesis Hydra