I think you're greatly exaggerating every hero "being messed up". Heroes have had issues, certainly, but I agree with kirblar that it has as much to do with the schedule as it does anything else. At the very least, you acting like this is a recent thing is disingenuous. There have been issues with basically every hero released.
That each hero comes out and has something hackneyed or soft/OP about them is hardly news. That's kind of how it works in my experience from virtually every game ever. I don't know that it should be called incompetence. Much like anything, they can only anticipate what we'll do with it and gamers by nature break things and once they do they only utilize the one broken aspect by and large while ignoring everything else.
Right before the start/at the start of the three week cycle, Sylvanas was OP. Blowing up creep waves, more damage than now, etc. You could argue her Cold Embrace is still stupid OP. Then KT came out and he was the most OP hero on release we've seen to this point. He's still one of the strongest in the game despite repeated nerfs. Johanna was also OP when her Condemn basically functioned as a planet's center of gravity, among other things including longer stun on her shield ult, but was panned when release. Leoric was also panned when released, but people quickly figured out he was not only OP with his respawn leading to cheese w/ Abathur, but that his general use as an actual hero was also very strong.
Kharazim came out and was shunned because his damage sucked, but it turned out he was actually good. And eventually got a damage buff. Then came Rexxar with his buggy Misha which was fixed within 2-3 weeks as I recall with the "1" button. He was never going to be more than a niche hero, however. Morales dropped and her health pool and survivability was too small. They gave her a slight tweak there and she sees play and was even regarded by some as OP less than a month ago. Artanis came next and his kit was questionable at best and his melee range was bugged. They've tweaked him several times and while many (including me) put him in the dumpster, people like Trikslyr swear by him. He's very much a Gazlowe kind of hero but for the bruiser role.
Cho'Gall dropped and he just is what he is. Fun to play and though in theory very strong he requires too much from your team to see a lot of play for folks like us. Lunara came next and had bugged attack animations, low health, and basically Nazeebo's damage without the utility. She's since been fixed in every aspect but the wisp and is now relevant at most every level of play. Greymane was next and there wasn't much of an issue He just suffers the melee fate, but thankfully can persist as ranged poke. And they went and made that poke even more viable. Now we have Li-Ming who is very strong. Bar issues with the orb pull or Disintegrate, she's still not at the obnoxious level KT or Sylv were in their heyday. She'll get those things fixed and just slot right in.
I doubt there's a hero released in any MOBA that doesn't have shit like this happen. It's part of the job. Every single one of the heroes released has some kind of issue - whether too strong or too weak or with a bug - acting like it's a recent thing is not very genuine. Either they've been incompetent all along, or they are developing a very fluid thing that will always require more hands-on testing than they can ever perform in house. And kit reworks are basically the same thing though I would agree those are less forgivable.
EDIT: And I'm not defending their releases or their patches. I'm just saying if you think it's bad now it's always been like this for whatever reason. If you have issue with it currently then you also should've had an issue last summer and the winter before that. Also, something is always OP and something is always UP and I think that is something that is largely forgotten on the internet in these discussions.