I agree that adaptations should have the same flavour, not necessarily the same content, as the books.
It's what made Dune a good adaptation imo. It tasted the same as the books, and used its medium to push them forward in new ways - for instance with the sound track.
Rand's about 19 in the books, and what... 25 in the series? A big difference.
What the series did to Mat was nearly as bad as what they did to Perrin, largely because it misses the entire 'flavour' of WoT - which, as stated above, is a coming-of-age tale involving simple country boys that
lacks GoT style grimdark stuff. The series is a testament to what the producers thought people wanted, not what was true to the source material.
What the series did to Mat and Perrin:
Book Perrin: gentle blacksmith's apprentice, a giant who thinks methodically and is careful with his strength.
Series Perrin: Married blacksmith. Problems with rage. Kills own wife in fight.
Book Mat: adventure-loving trickster who is not as charming as he thinks he is. Seems entirely concerned with self, but displays nobility when others are in danger. He milks cows for his dad and he loves his sisters.
Series Mat: Mother is a drug/alcohol user. Father is an adulterer. Mat is a thief who steals for gain.
You can see how, with these characters at its helm, the series just doesn't feel like WoT to me.
I'll add the caveat that I only managed to stomach two episodes and then had to bail. So maybe it improves.