#and don't pretend that it WOULD be an exception to reprint it just to make it Pioneer legal

[21st-century-minutiae]

In the early twenty-first century, Magic the Gathering is a popular trading card game. The game has multiple official formats which define which cards are legal to play, to create different experiences. Pioneer is one of the newer formats, which generally allows cards that were created after 2012 to be included, with some bans.

Ancestral Recall is a card from the original 1993 release of Magic the Gathering. It allows a player to draw three cards at instant speed at the cost of "1 mana." "Instant speed" means that you can play it on your opponent's turn. This is contrasted with "Sorcery Speed" which means you can only play it on your own turn. This is generally a powerful option since you could wait for your opponent to take their turn before deciding what to do, and because it doesn't allow your opponent to react. "Mana" is a resource in the game. Generally speaking, more expensive cards are harder to cast and need to be played late in the game. "1 mana" cards are VERY easy to cast and can be used as early as the first turn. Because drawing cards is VERY useful in Magic, and because Ancestral Recall is very very very easy to cast, it is considered one of the most powerful cards in all of Magic's history and is banned in most formats, including Pioneer.

Treasure Cruise is a card from the 2014 release of Magic the Gathering. It allows a player to draw three cards at the cost of 8 mana, but it also has an ability to make it cheaper at the cost of doing some setup, to a minimum of 1 cost. If you build a deck in the right way, it is pretty easy to make Treasure Cruise a 1 mana spell that draws three cards, which makes it often seen as comparable to Ancestral Recall. However, there are a few key differences:

First, it does require setup to use. Even if it is relatively easy, this setup cannot happen on the first turn of the game (except in VERY weird circumstances). Second, using one copy of Treasure Cruise undoes your setup for the next one. Ancestral Recall can draw another Ancestral Recall which can be used immediately, as early as turn 1 or 2. But it will be somewhat later in the game before you have enough setup that you can play multiple Treasure Cruises in a row. Third, while pretty much every single deck can play Ancestral Recall (indeed, it is almost mandatory to play the card whenever it is legal), only some decks can properly setup Treasure Cruise to make best use of it. Finally, Treasure Cruise is NOT at instant speed. You have to commit to playing it on your turn. Even in the best case it is not as strong as Ancestral Recall for that reason alone. Treasure Cruise is a very powerful card, but it is not as ludicrous as Ancestral Recall. It is also LEGAL in Pioneer.

"Splinter Twin" was a powerful and popular combo from the "Modern" format in magic circa the year 2013. Modern as a format which permits most cards that were printed after 2003. The year 2013, where there were about 10 years worth of magic cards, was considered something like the height of the format, and is often compared to the current Pioneer, which also has about 10 years worth of magic cards.

The Splinter Twin combo made use of two cards. The first was the titular "Splinter Twin" a '4 mana' 'sorcery speed' card which permanently gave a creature the ability to make temporary copies of itself once per turn. The second was any creature that could let a creature use their 'once per turn' effect again. With those two cards together, you could make a copy, have the copy refresh the copier, make another copy, have the new copy refresh the copier, and keep going infinitely. This let you do infinite damage as early as turn 4 of the game, assuming your opponent couldn't disrupt you. Waiting until a later turn allowed players to prevent disruption pretty consistently. This combo was banned in 2016 from Modern, because it was very popular at the cost of other decks. Many people felt this banning was a mistake, especially in retrospect as the format only got more powerful. Splinter Twin was never legal in Pioneer.

The asker in the post above is inquiring as to why Treasure Cruise is legal in Pioneer, but Splinter Twin is not. Calling Treasure Cruise "Ancestral Recall" is a provocative effort to hyperbolize the card, and calling "Splinter Twin" a "turn 4 combo that dies to removal" (removal being a term for getting rid of a creature which would disrupt the combo) is an attempt to minimize the power of Splinter Twin and ignore the fact that it was printed before 2012, meaning it is not currently eligible for Pioneer. The implication is that if a card as powerful as Ancestral Recall is legal, than something that is weaker like Splinter Twin should NOT be legal.

Mark Rosewater, an individual who designed a lot of Magic the Gathering, denied the premise that Treasure Cruise is Ancestral Recall, implicitly stating that the probing question was made based on a flawed premise.

In the early twenty-first century, Magic the Gathering players familiar with the Modern format of 2013 (of which many older players would be) would likely know that both Treasure Cruise and Splinter Twin are being mentioned here, despite neither card being mentioned by name. They would understand the description, know about the formats, and know what Ancestral Recall does. They would know who Mark Rosewater is, and likely have an opinion about Splinter Twin (and Treasure Cruise).

People NOT in the space of Magic the Gathering, of which the majority of the early twenty-first century would be categorized (as, while popular, the card game is not universal) would have zero idea as to what is being discussed in this exchange.

Why is ancestral recall fine for pioneer but sorcerery speed infinite damage, turn 4 combo that dies to remove, isn't?

Ancestral Recall is not legal in Pioneer.