so the biggest issue (for me at least) is the mastery 6 and mastery 7. in order to make them you need to get tokens from playing well on said champ, which is completely fine and makes perfect sense, but it has a high BE cost, but you can ignore this cost by using a shard which is disenchanted to get BE. So now we have a system where out BE which from the numbers show a roughly equivalent gain of points to the old system, but that is only if you disenchant the shards to get said BE to use instead of saving it for mastery tokens or possibly a discount champ.
so since you are likely to be saving the shards for possible mastery since that 90 BE warwick shard would save you a huge amount of BE by using it for the mastery, it makes sense to hold on to it instead of turning to BE since a 2450 for mastery 6 and 2950 for rank 7 make using it for disenchanting feel like you missed out are punished for needing them while saving the tokens just means you get no BE in hopes of getting the shard and tokens to get the emote for that character or your favorite character.