I agree with you. There is no reason to release new champs, we have enough already. And we have already a lot of champs with practically the same skills with different visuals. But I think that the inability to balance the game is on purpose, to keep on some rotation to encourage players to buy newer and newer champs and skins. Though as I see it's starting to hit back as I met many people who turned away from the game or simply just stopped spending on it as they know that their new champs and skins will be unplayable soon anyways.
As somebody coming from DoTA not so long ago I'm suprised how small the viable champ pool in LoL. I meean in DoTA about 90% of heroes are picked in pro level play while in LoL how much is it? 20% at best? Imo they shouls stop this practice and start to balance things finally for real.
But when they balance something they do it in a quite weird way, making the game more and more bland. I mean, a MOBA is abou to pick champs/heroes what are very good in some things and very bad in others and try to work together with your team to synergise your strong sides and to defend each others weak spots. But it seems like in LoL they are trying to make everything more flat and soom everybody will counter everybody and nobody nobody.
For example: If a champ is too fast and too strong, Riot balance it a way that equally decrease it's speed and damage. But it still will be a bit better than the rest so it will be an obvious pro pick over others. And there won't be perfect balance this way until every single champ will be about the same by all means. That isn't the way how you balace things in a MOBA. If the champ is too quick and strong then decide do you want it to be a quick or strong champ and for example decrease just it's speed. And if it turned to be weaker than supposed then don't give back speed but increase it's damage. I'm sure you know where I'm coming from with this.
But there are other weird things in the balance, probably because Riot tries to design a game for the many egocentric soloQ players out there. Though it's an impossible task to design a perfectly teamplay-based game - a MOBA - to players who want nothing else but solo carry.
For example again: It is strange how limited hard CC, healing, invisibility etc. abilities in LoL already, especially compared to thing like how ridicolous amounts of lifesteal you can build. Everybody seen assassins jumpong into a 1v4 with low HP, killing two tanks easily and coming out with full HP, ain't it? Weird.
Well, I'm trying to explain this with an actual issue finally: assassins. In DoTA (sorry but that's what I'm familiar with that's why I bring the counter example from there) there is e.g. Bounty Hunter, a typical assassin. His kit - as I suppose you aren't familiar - looks like something like this: His Q is a shuriken toss with some damage and a small stun with some medicore range, his W is a passive giving him 150-225% critical strike bonus and deals 15-30% move and attack slow for 3 sec on the first hit of a target, his Q is a 20-35 sec perfect invisibility with 30-120 bonus damage on the first strike braking the invisibility and his R is Track what marks and enemy, making him always visibly and even the amount of gold he carries (it matters in DoTA, I won't explain now why) and it gives 16-20% bonus move speed for you and your nearby allies and gives bonus gold top you and nearby allies if you kill the marked enemy. Sorry for the details but I hope this way you see that how they reached with skills and passives that Bounty Hunter can pretty much kill any isolated target with a gank, having a huge burst damage in that case, but otherwise he suffers in sustained fights and basically in teamfights. As this is what an assassin is for after all, isn't it?
But how LoL dealt with the assassin problem? They can't do enough damage to successfully gank? Well, give them more damage. Oh, they have more DPS than ADCs and brawlers? Well, then let's implement lethality as a solution. Oh, other damage dealer champs can exploit lethality so badly it hurts... Then what to do? Well, then just forget about what an assassin is meant to be basically and help their survivability with giving them too strong lifesteal items. And after all of these just say that we are sorry about the long queue times and we really don't get it why everybody tries to play burst damage assassins and nobody supports who are very happy if they have some 1-2 sec CC :-)
Anyway, I do apologise for the long reply but this balance issue bugs me too. And don't get me wrong, I like LoL an I think it is a big improvement in many aspects over DoTA (even if it sounds weird from me, based on the popular archtypes). But what the balancing team is doing nowadays (I can't talk about past times, I wasn't here) is a. They don't really have a clue how to balance a MOBA game at all, b. They are pushing so much that artificial "meta rotation" and just doing a mess with it and making everybody upset sooner or later.
Just my personal opinion ofc.
as the most picked champ in that role. This may be because of how 
works with him really well. Not only that but before the lethality change there was a problem with adcs building armor penetration. Not only that but riot forgets about some adc who didn't have a big rise (
). Also currently riot is trying to insensitive building crit like with 
but it comes at cost by making 
's power spike coming faster (talking about the lowered cost of 
on the PBE). And as for killing a champ cough
cough because the pros abuse the champ is saying, at least to me, we value the real people who make this game money.
and 
had some type of unification buff that when they are together they do increased damage, idk I am not a game designer. Or like when 
and 
have like the void-lings follow and respond to some of rek'sai's attacks since the are both from the same place.