I know you're not saying this, but some posters on GameFAQs and Reddit have said that people are whining that they can't get everything in a week or a month and move on. That's not the problem. Grinding is fine. The problems are twofold:
1) If I really like a skin, I can only know whether it comes from Krypt or Towers of Time. I can do nothing but wait for RNG. I cannot plan and specifically grind for that skin like how you can repeat the same missions for their drops in Destiny or Diablo. Tell me that a particular skin has a 5% drop rate in my Klassic tower, and I'll run that fucker till I get it. But as things are now, the Krypt is completely random, Kollector's exchange inventory in the Krypt is completely random, in game real money store is random, the timed towers that show up are random, and no one know where tower keys drop. So you are essentially unable to hyper focus on grinding that one skin you want, and it would take months for it to show in one of these avenues, if you even get it ever.
2) Towers of Time gatekeep players from lower skill levels and their drops are impossible for the vast majority of the playerbase, which consists of casual to semi casual players who do not have the time to 'git gud'. Even if they git gud, the bullshit towers still gatekeep a lot of progress.
So the problem isn't that you can't get everything at once. It is that a lot of players won't even get what they want in the time they play this game, may it be a couple of months or a couple of years.