That's an interesting point you bring up and while I say that I'm not a fan of the new companions, that doesn't mean I want the old companions back, although I would love it if Misty came back because her and Ash were always the main characters of Pokémon to me. However, I'm at least happy that the other characters are moving on with their lives and achieving.

Misty - She set out to become a great water Pokémon to prove to her sisters that she is just as good as they are. Now she is the head Gym Leader at the Water Pokémon gym.
Brock - Set out to become a Pokémon breeder and discover that he actually had a passion for helping and healing Pokémon. So now he's home studying to be a Pokémon Doctor.
Tracy - Was a Pokémon watcher who always admired Professor Oak. Now he's Professor Oak's assistant.
Gary- Started off as an arrogant kid who wanted to be a Pokémon master. Now has matured and realised he wants to be a Pokémon researcher like his grandfather.
May - Started off not even like Pokémon and just using them as an excuse to travel. Discovered that she was interested in becoming a Pokémon Coordinator and has the confidence to travel on her own.
Dawn - Similar idea to May with some differences.
Max - ......moving on.

So I'm happy that some of the characters are moving on and achieving something with their lives. However, that doesn't change the fact that I find these other characters annoying.

Iris - When newer fans praise her and bash Misty (Not all of them) I don't get it because she is a very similar character to a certain point.
She specialises in dragon Pokémon, similar to how Misty specialises in water Pokémon.
She is afraid of ice Pokémon, similar to how Misty was afraid of bug Pokémon.
She teases Ash and calls him kid... kind of like how Misty did.
She's a Gym Leader in the game..just...like......Misty.
She carries her Pokemon Axew just.......like.......Misty........did........with........Togepi.

So to a certain point they are similar characters. However, there is a big difference in the way they interact with Ash.

The way Iris comes across to me is a bit of a bitch to be honest. She is always talking down to him and calling him a kid. I wouldn't mind it if it was once and a while but she does it all the time. Even when he is asking for advice or offering to help her. After a while you start to think "back off".

Some people make the argument that Misty use to be hard on Ash in the first season of Pokémon which to a point might be true, although I don't remember Misty being quite that hard on him. However, if you remember in the first season Misty didn't even have much of reason to be nice to Ash. When she first started travelling with Ash she didn't like him. She was travelling with him because he stole and destroyed her bike for the most part. So this guy took away her method of transportation so he owes her. Then gradually over time she grew to like Ash and consider him a friend. Sometimes she would still tease him or call him out when he did something stupid but most of the time I feel when she did it she he deserved it. Ash sometime needs someone to shake some common sense in him to tell that he needs to smarten up. But there a difference between shaking common sense into someone and being mean, which Iris is.

Then when Ash and Misty went to the Orange Islands you could see the dynamic of there relationship change from friendship into something more. That's really were the more romantic side of there relationship really started to develop. Also when Ash was in the Orange Islands you noticed that he really started to smarten up as a trainer through allot of the different experience he had through his adventure there. Because of that, when Ash went to Jhoto, he actually came across as a really smart trainers, which you saw in those episodes were Ash would be teaching younger trainers (Until Advanced were they slow started making him less intelligent to the point where we are now where he comes across almost like a beginner again). BUT, Because of that and the fact that Misty had started to develop feeling she was nowhere near as harsh as she was when she first started travelling with him.

Ash didn't ash Iris to come or even do anything were she should follow him. She made the choice to travel with him. So you'd think if she was making the choice she wouldn't just cut down the guy at every opportunity she is given. She also doses it in such a condescending way. It might be due to her voice actor but I doubt it because her facial expressions while doing it also look condescending. If she is going to be like that I don't see why she doesn’t just not travel with him if she doesn't like him so much.

Plus, she calls Ash a kid but she act more immature then he does. Seriously, she careless and gets them lost half the time. When Misty would call him immature it's because he was acting immature and he deserved it. Also she didn't not act as immature as him. People in glass houses shouldn't throw stones.