I would say that in average, the characters change are a plus for the player.
-Gold costs were increasing incredibly quickly for skills (it was over 38K for lvl 7), while the shard price doesn't increase as quickly (60 for the last level). Also, if you get shards on the side, you can actually spend them, unlike before, where you were so restrained by golds you didn't use them.
-You have much more runs to get shards (5 runs at 40% instead of 2)
-Shards drop in hero mode as well (10 runs at 16% chance instead of 0)
-So, basically, if you focus on one character, before, you have 2 chances at 40% for an average of 0,8shards per day, now you can spend up to 200 stamina to get an average of 3.6 shards per day.
-The money was a real bottleneck, and now, it's only required for three things, tower upgrades, star upgrades (not really required much since the bonus are currently quite small), and money gacha (which can also gives shards). We will be able to throw money at the money gacha much more often for mats, skip tickets and things like that.
However, yes, I agree with you on the fact that the 2nd and 3rd slots have to be paid is quite a wrong decision. However, I have to say to the game credit that it gives a huge amount of gems (enough to unlock the 2nd and 3rd slot) while still allowing you to get everyone, and get them quickly. I have already everyone unlocked. I still don't think it's P2W, unlike most games on Nutaku.