I did played his games since GBA up to the DS ones including the PS2 ones as well but IMO non of them seems to exceed SOTN's level.
I think this here is a big part of the problem for you, based on everything you've said. You seem to think that it is somehow
wrong that SOTN was never matched or exceeded by the artists behind it.
SOTN is definitely Igarashi and Co.'s magnum opus, their masterpiece. It is their pièce de résistance, chef-d'œuvre, a tour de force of games production. A sad thing about masterpieces: by definition, they will never be equaled.
The Last Supper, The Creation of Adam, American Gothic, The Night Watch, The Wedding at Cana, Luncheon of the Boating Party, A Sunday Afternoon on the Island of La Grande Jatte, The Garden of Earthly Delights... these are all masterpieces. But we don't call everything made subsequent to these works crap. We don't denigrate Michaelangelo or Da Vinci for never matching or exceeding their finest work in later attempts. It's a factually incorrect argument that artists should improve on every work, or that when they peak, they maintain that level of quality. They're people, not machines. Improvement is definitely the ideal, and we do try to match our best works every time afterwards. But most of us fail in both.
Iga actually got pretty close with a couple games:
Harmony of Dissonance, Aria of Sorrow, and
Order of Ecclesia all come within spitting distance of standing where Symphony did, but were kept from it largely due to key practical limitations of development for each: money, time, less broadly powerful hardware, a corporate production structure that steadily became
actively hostile to their own developers, etc.
Unfortunately for everyone, he was never again able to summon up that perfect storm of talent, resources, and time that allowed Symphony of the Night to be as perfect as it was. It was a one time deal, a moment of utter perfection. The cost was Koji Igarashi's Greatest Work came relatively early in his career, a fact which he admitted well before the series started declining. It stayed the ideal for him though, and even knowing he could never recreate it, he at least tried to take the best aspects that people liked and incorporate as much of those into the watered down versions Konami kept asking for.
Not everybody appreciated that. Reviewers definitely didn't. And by Portrait of Ruin, most of us fans were actually pretty done with it as well. If you dig up old forum posts from back then, a ton of us
were not happy that the quality had sunk that low and become so paint by numbers. We thought it was developer laziness at the time -- the behind the scenes drama of working for Konami wasn't widely known then, and wouldn't be for almost a decade. And there definitely was a degree of tiredness, looking back. The team was worked hard, long, without much in the way of breaks or vacation time, and constantly berated by
everyone, including us fans, as to why we weren't getting something so good as Symphony over and over again. Iga, in particular, looked like he wasn't getting a whole lot of sleep in press photos from the time.
His apology, and a lesser masterpiece, was
Order of Ecclesia which was all the essentials we'd ever asked for. As the last game which he had majority creative control over, it's one hell of a final work. True, there was some... I'll be charitable and call it "mixed results" after like Harmony of Despair, but his sheer level of creative control (versus having his name slapped on a final product he had relatively little to do with, much like Hideo Kojima and the first Lords of Shadow) is still questioned, so we tend to consider Ecclesia his last "real" work.
The simple fact is that he peaked early due to exceedingly favorable conditions he had no real control over. That's how a lot of artists are.
I know I sound like an apologist, but I'm writing with the benefit of hindsight here.
I used to be right where you are. And had the insider knowledge of how Konami operates not come to light, my opinion of the lesser entries in his run (Judgment, Dawn of Sorrow, Portrait of Ruin, etc. al) would still be largely negative. As it is, I have the perspective of a long term fan who's learned a lot about games production in that same span.
That's why I'm so quick to jump to his defense. That's why I'm asking that you reframe how you look at the series. It won't make the bad games any less bad, but context can change a
lot, and make it easier to appreciate what they did do well, as opposed to fixating on what went wrong.