I know I'm a bit late to this topic, but I figured I'd respond anyway because I think I have a slightly different perspective to offer:
I am also on server 1, but my guild has been #1 in Guild War Rankings for 14 straight weeks (#2 in total power, #1 in team power, #3 in stars, #1 on all servers for the Birthday Bazaar Contest), my player age is 377 days, and I'm currently VIP 7. For the first 10.5 months I played, I spent 0 money (outside of the occasional monthly deal funded solely by Google Opinion Rewards) but have spent $60 in the last month and a half or so. Despite the lack of spending (compared to other top players), I regularly finish in the top 10 in challenger in FP every night and sometimes in the top 10 in Coli challenger (that one is harder to achieve since I am generally fighting people with 10%-20% more power than me). Given how FP is, that's largely just due to the fact that I'm on the east coast and can time my attacks when other top players not US based cannot.
Anyway, the whole point of this is simply to point out that I'm probably not the typical casual player. And I'm not in the typical casual guild. We have a handful of really big spenders, but the majority of players are in that middle range (VIP 7-14 I believe).
Issue #1: Too many characters released every month
This is only an issue because of power creep. What I mean by that is nobody would have cared if they released 4 heroes, or even 10 heroes, every month if the older heroes stayed relevant. The "problem" is that new heroes are generally pretty OP. Revenant, Spider, Plant, Cyclops, Thief, etc are all basically a must-have at this point. If their power were in line with every other hero, you could choose a couple here and there to work on in your spare time. Instead, they are better than the old heroes and you basically have to rush them to keep up with the other top players/guilds.
However, let me offer 2 other perspectives:
The "Big Spender": 2.7 was released two weeks ago, and I am still working on gearing up my Revenant (P4 atm). However, there were a large number of people on S1, both in my guild and not, who had Revenant or Banshee up to max gear level in a day or two (and 5* as well!). Releasing heroes at the current pace gives them something to look forward to and work toward; it gives them an advantage (which they should have, given their $ spending), too, because they get the OP heroes before anyone else. I know the typical saying is it's better to have 100 minnows than 1 whale, but remember that in DS the VIP scale is not linear, so people who are in the VIP 18-20 have spent many more magnitudes of money than those in the VIp 7-14 range. It's important to keep those types of players happy, engaged, and spending money on the game.
The "New Player": So my brother recently started playing. Rather than start on one of the newer servers, he joined S1 so he could (eventually) be in my guild. He's currently level 65, slowly working his way up. At one point, I was concerned that he would be at a disadvantage because he missed all the good old heroes being in shops - Ninja, Mega, Understudy, etc. But recently I've realized that the release of new OP heroes actually gives newer players a method of catching up and being able to compete with older players. He doesn't have to go back and work on Mega or Understudy or the OP heroes of yesteryear. He can simply work on the heroes currently in shops and be competitive with them.
Issue #2: Some characters are better than others
This is basically tied into issue #1, but I disagree with some of the language in the original quote. Who has ever said that all heroes are equivalent in power? I've never seen anyone from PB or GREE say that. There are obviously heroes with different power levels; it happens in every game and it is impossible to avoid.
PB does do some hero balancing (see the nerfs of Rabid, Bro, Pixie, Hydra; see the recent patch notes of buffs to Rabid, Roller, Pirate, etc) outside of giving older heroes orange skills to try and make them relevant. They could probably do a better job of this, but remember - even games like League of Legends and World of Warcraft, which operate on a much larger scale and budget, struggle with keeping every hero/spec relevant and equally powerful.
Issue #3: Not enough time given to fully explore a new hero
This is basically the same as #1. Heroes released at a pace that some people cannot keep up with. However, @Little_Snow did bring up something that I do think is a reasonable complaint:
The speed with which promotions and level caps are raised. Thankfully 2.7 left those alone, but before that we were getting a new level cap and promotion every month. I hit 100 a few days before the level cap was raised to 110; I was out of potions and out of gold from leveling the heroes I used. And there were still people in my guild who hadn't hit the cap before it was raised!
If my guild, filled with a bunch of try-hards cannot (or barely can) keep up with the level caps/promotions, they are being released too fast. From my perspective, every other month is a more reasonable pace; I've gotten to the point where I have 15 heroes at O3 (12 with full gear) and have even been able to start upgrading heroes I don't use that often or who don't benefit a great deal from promotions. I have some potions stockpiled and am sitting on 60 million gold.
Perhaps every other month is still too fast for casual players, but remember that you have to give top level players something to work toward.
Issue 4: Crypt is too hard
I honestly am not sure what to say about this one. We have a 6 skull limit in crypt until 3 hours before end. I typically do my 6 skulls at 9 and am done within 10 minutes. I hire a hero and then use 1-3 of my own; the only time I ever use a full line is if there is a Bone Dragon and the power is 80k or higher. If nobody hops on for FFA, I can easily clear 30+ lines just by hiring a hero and throwing in a single one of mine.
The only thing I guess I could offer is that you should make sure the people in your guild are posting good heroes to hire.
I've been in my current guild for over 6 months. During that time, a few people have left. This happens in pretty much any game though; there has not been a mass exodus of players from my guild. We are still having fun pushing ourselves to stay #1. I still enjoy the challenge in Coliseum and FP, trying to beat players who have 10-20% more power than me.
By picking and choosing which heroes you invest in, the deluge of heroes becomes a little less overwhelming (e.g. don't waste resources on Doppleganger). But I agree that the release schedule of new heroes is a little too fast; the level cap and promotion should not be raised every month; and it would be great if they did a little more balancing on older heroes to keep some of them relevant.