It’s less about “what’s in the pool(s)”, and more about “can I get stuff that isn’t in the pool(s)?”
The only characters that are 100% unavailable from regular tokens should be Yelena (vaulted due to obsolescence), Bag-Man (same), Devil Dino (special occasion character), and Howard (same as Dino).
They want to put pools on Heroics and Event tokens and even Vaults, I don’t care. Making it so Heroics only have the latest 12 4*s is actually a neat way to encourage the new characters, and make them slightly easier to cover.
But everyone should be available, somehow. The old classics, as dilute as they were, worked because ALL 4s were an option (minus the aforementioned special two). For 5s, it worked because classics and latest covered everyone. No single pack had everyone, but between the two they did, so you could pick and choose based on who you wanted.
PVE events have three essentials, one each of 2*, 3*, and 4*, PVP requires a 3* the vast majority of the time, DDQ requires a 3* each day, a 4* every 5, and a new combo of 2*/3*/4* each day. Those factors encourage a broad roster. The Champion system allows you to take a character fully covered (13/13), and continue to level them with the next ONE HUNDRED COVERS you acquire for that character. Advancement encourages repeated collection of covers. Thus, the most desirable outcome as a player is to acquire a large number of ALL covers (ISO non-withstanding).
So that’s what matters. Whether in a single token or in a series of pools, all characters should be available. This is most glaring with the 4s, but I believe it applies to the 3s as well. Simply having two Heroic tokens, each with half of the available 3s, could fix that problem. A classic legendary token with all 4s could help things there, regardless of whether or not the rest of the tokens have pools or not. If they go for the latest 12 4*s in Latest Legends, it doesn’t matter as much if those 12 are in the Classic Legends, so long as everyone else IS in the Classic token.
The problem isn’t the pool, it’s getting to play with everyone not allowed in the pool. Getting weird with how you pick pools does not fix the problem of having pools in the first place.