This wasnt as useful once the Tag Team Pokemon were released, however, as those also had really high HP and forced decks to adapt to that
There are plenty of spells that offer one mana for two damage or two mana for three damage but there are fewer that do four at two making it that bit more unique
As such, more modern cards can defy this trend, or even reverse it, and the Special Illustration Rare Terapagos ex from Stellar Crown is a perfect example of the latter
But to make that ability available for just two mana a tiny fraction of what might be available to a player at the time ensures that Time Walk can steal a match in completely unfair ways
At the same time, the Hero deck required fewer lands, which meant that the Rat deck was more likely to get mana flooded (by virtue of needing to build with more lands in the deck)
Put each of those cards into your hand instead if there are three or more Lesson cards in your graveyard