With BE and IP combined, it becomes really clear how overpriced Mastery 6 + 7 are

3250 BE

That's how much it costs to take two Mastery 6 Tokens and turn them into Mastery Level 6. This really didn't seem like much when BE was separate from IP, but now that the choice to upgrade Champion Mastery directly takes the same resource as unlocking new champions (and rune pages, which are still a thing for some reason) its really plainly obvious that it costs too much. 3250 is over half the 6300 ip that a new champion costs the week after release. Mastery 7 costs 3900, exactly half of the cost of a new champion on release day.

To be fair, unlocking mastery 6 + 7 did conflict with progress on unlocking champions before, abeit more indirectly. Disenchanting Champion shards into BE for Mastery meant not using that shard to reroll into a new champion. But at least if I wanted to do that before, I had another, unrelated resource which I could use for champions (and rune pages) that wasn't being affected by my upgrading mastery (IP). From now on, every time someone wants to upgrade a mastery, that's half their progress to a new champion gone.

This isn't that big of an issue for me personally, because I own all the champions now. But for new players, Mastery levels 6 and 7 are going to be a literal trap that makes them waste valuable currency they could be using to unlock new champions (and rune pages, which still exist for some reason).