Yeah,
@onering has it right. There have been
EDH-focused cards printed in Standard sets, and
eternal-focused cards in Commander decks, so drawing any sort of line based on 'design intent' is a fool's errand.
That said, something else I'll call out is that supplemental sets bring a
ton of intentional power creep. Standard has rotation, which means that WotC can keep its power level relatively flat and still have new cards be relevant. On the flip side, a lack of rotation means in eternal formats, it becomes much more difficult for new cards to be relevant - instead of competing with the 1,500 or so cards in Standard, they need to compete with 10x that amount in Modern, or even more for Legacy or Commander. As a result, if WotC wants to print new cards to be relevant in an eternal format (and the existence of Modern Horizons and Commander Legends strongly suggests they do), they pretty much have to introduce power creep for those cards to stand out. That's how we end up with stuff like
Ragavan, Nimble Pilferer and
Dockside Extortionist.
So, not only are we getting more new cards, but we're also getting cards at a higher power level. The net effect is a soft rotation as newer, more powerful cards push out older, weaker cards. To be clear, rotation isn't necessarily a bad thing - it keeps formats fresh and interesting, and means that there will always be new experiences... but
that isn't why I come to EDH. I like building decks, mastering them, and having them be relevant forever. EDH is designed to be a high-variance format - 100-card singleton plus everyone having their own set of decks is already more than sufficient to stop it from ever becoming stale. Instead, it feels like WotC is forcing EDH to be like Standard, where you're forced to swap out half of the cards in your deck every year if you want to stay relevant. That may be good for WotC's bottom line... but personally, I find it exhausting.