All high end MC brands sound different. Most of these sounds are truly excellent, just different. Koetsus have a particularly distinct sound (on the side of: voluptuous & full bodied, with a very vivid midrange), and are extremely good at what they do. That doesn’t mean they’re "the best" in an objective sense - but they have a vehement fanbase for good reason.
Years ago I didn’t buy the hype, and thought Koetsu’s pricing was outright stupid. Then I actually heard one (on loan, in my own system no less) - and that’s when they get you! I was blown away - expectations absolutely shattered, and I couldn’t box up my Ortofon Windfeld MC fast enough lol. In fairness, my system at that time was absolutely dying for some injection of warmth (Windfeld was a terrible match), and the Koetsu Onyx swap-in gave not only warmth in spades, but an overall quality boost as well.
These days I’m enjoying exploration of other MC’s. AirTight, MSL and Van den Hul are the newest on deck. All superb. But the Koetsus in my collection will always be like family.
Also, you can get a quality used Koetsu for $2K. You’re buying the seller as much as the cart itself.