It's still a plot point that's able to be critiqued.
That doesn't mean it's good criticism or even warranted. Anyone who is complaining about Sanji not poisoning the cake, completely lacks the ability to understand his character, or any character for that matter, even on a basic level. You can't just make characters do stuff that goes against their essence on a whim when it's convenient. That's not how it works.
When Sanji was introduced in the series, he fed a starved and dangerous pirate crew, knowing full well that this could severely backfire. Yet he did it anyway. In this chapter we were treated with an echo of that with Zeff feeding a bunch of louth-mouthed pirates saying he will feed anyone that is hungry. For Sanji cooking might as well be a religion, an ideology or a mantra, it's not some shallow principle.
So people who think that just because of this situation he has to betray his way of life, shouldn't be criticizing as they simply lack the ability to do so properly. They are just complaining for the sake of complaining, completely oblivious about what it is they're actually saying.
Seriously expecting of Sanji to poison his food just because you think it's practical in this specific situation, is like expecting that Zoro will throw away his swords and will start using guns just because he encountered an opponent that has an advantage over swordsmen: it's messed up and screws his character up.
Let the after whole cake island bounties commence lol. I predict the following ( this was prob discussed earlier but i wasnt there so yeah ):
Nami: 66 million > 102 million beri (shes done alot)
Chopper: 100 > 200 beri ( lets keep the gag going )
Carrot: No bounty >150 beri (she'll be considered another pet, doubt they;ll go to zou just to drop her off)
Brook: 93 Million > 176 Million beri ( facing big mom and stealing her poniglyph)
Jimbie: 400 million > 520 Million beri
Sanji :177 million > 328 Million beri ( just to annoy zoro and make him go all out in wano to prove himself stronger )
Luffy: 500 million > 700 Million Beri
All of them just had an increase, this despite the WCI-group (excluding Luffy) leaving Dressrosa halfway through. If they would receive yet another increase, which I highly doubt, the whole crew would receive one.
At the very best Jinbei is possible as he hasn't received any increase since Marineford and Luffy maybe by virtue of him being the ringleader. There's a slight chance for Sanji, but that's purely because his previous bounty had been 'tampered' with. For all the others there is absolutely no reason to change anything.