I mean, the devs finally succeeded in pruning all the bits of the game they say "ruin Magic."
Except it turns out the Magic that's produced without those bits? Pretty bad.
But I wouldn't let that take away from your friend's win. Anyone winning a GP put in a lot of work (and probably exhausted their luck stores for a while as well!), and deserves respect. While this standard isn't particularly diverse, the mirror matches are often brutal on incorrect play-line choices.
It's also kind of hard to think about format diversity without considering the context of sheer card numbers. Magic sets are just smaller than they used to be. It's easier to have the nutty diversity of kamigawa and original ravnica when their cardpools were between 1.5x and 2x as large. The % of competitively useless cards in a given set has remained pretty consistent, but it's now out of a much smaller pool.
They definitely need to spend less FFL testing time on "Well, do theme decks using the set's new mechanics function?" and more time on seeing whether the mana bases are too powerful, and whether these "Marquee" cards can be pushed to broken (which they have been, or close to it. Sell them packs-err, I mean READ DAT STORYLINE).
Magic's so much more enjoyable when the power-level is spread out across the set. This trend towards concentration of power has been a downhill slide since they introduced Mythic Rarity (with Khans of Tarkir being a very fun outlier, where the power was pretty evenly spread across the set).
My "Eve of the Announcement" Ban Prediction: Felidar Guardian ban, since StandardTwin constrains deck-building heavily for the next 1.75 years, even if it has moments where it's not actually great.
And that's where I'd stop, but judging by their last ban discussion, they'll also ban something from Mardu and B/G, so let's guess Heart of Kiran and Snake for maximum playerbase rioting.