Not totally that tbh. It depends on your board. I was able to go to as low as 650 coupons per shisui frags. For example, in the board you showed, you have way more items that are "common" than "rare". This means these drop more often and lower the drop rate for shisui. Normal dust, magatama, bells, stamina potion and mood scroll are considered "common" items iirc.

Before I'm asked to share, here's the board I had. Of course, I did quite a few refresh to get this board. So it really goes down to how many refresh you do and how badly you want to play with RNG.

What are considered "rare" items?

We're a few staff from the Discord team that did a lot of boards. Personally, I tested around 12 boards since the event was out in April.

Rare items include : Charm packs, refine packs, seal scrolls, cloth, threads, summon scrolls, cave keys, and gold dusts.

this event stands apart from others as it seems to have 2 levels of RNG.

one is drawing a random reward from the board. you may not get what you wanted, but you do at least get something and that something has value. that mechanic is pretty consistent with other events in this game.

the other level of RNG is refreshing the board itself. there are no rewards for participating in that RNG action and you can easily spend 1k coupons or more without ever seeing shisui, never mind seeing him on a good board. unfortunately, unless you are very lucky, you have to get through this level of RNG in order to participate in the other one, and that makes it a much less rewarding game mechanic overall.

If we can get 650 coupons per Shisui fragments in that other board that would be much more worth, in my experience it was around 900-1000 coupons per fragment with the board I showed

I dont have screenshots to throw in here but I will chip in with my experience. This is just my personal experience not advice one way or the other so hopefully it wont be taken down for "drama". But personally unless picklejuicy comes back I do not trust the numbers and claimed drop rates given here or discord.

In a fateful choice event kushina summer was stated to be around 13k coupons to recruit, I spent 18k and only got enough points for 30 frags

I got a jackpot x from slot machine and was told instead of getting shisui directly it would be better to take the coupons, wait for a good cycle and that I could get shisui for under 100k from capsules plus rewards from any fuku at the time. I already had coupons saved before the jackpot so I could afford to be a bit careless and test. Over 2 capsule events and roughly 9 different shisui boards 55k coupons got me just 13 frags.

I also went for edo itachi because I only needed 3 frags to 4 star him, I refreshed until getting what the mods told me was a "good" board, i spent 10k coupons and got just 2 frags

well, i guess the question that comes to my mind is, what's the refresh drop rate for good boards that include shisui? because the drop rate for shisui once you have such a board doesn't matter if you can't get such a board in a reasonable amount of attempts.