Is Arcanine still worth investing?

Arcanine is still a Lapras killer

Arcanine is still a powerful attacker. I'd hold off for a few weeks and see how the metagame goes. But I still like Arcanine and would power up at least 1 for attacking.

Your other options for large fire attacker are Flareon (a little bigger than Arcanine now) and Charizard (a little bigger than before, but still smaller than Arcanine). However, Fire Fang is still a little better than Ember (under 2s so you can fit at least two in between dodges) so Arcanine is still overall a better fire attacker.

Definitely with those moves and IVs! Although Flareon now ranks higher on CP, it still lacks the tankiness of Arcanine. And if you are dodging with Flareon, ember is a very tricky move, since the cooldown is just over a second. Against most defenders you can only squeeze in one shot safely between dodges and if you don;t dodge you don;t have enough HP. So fire fang (2 safe attacks as pipjay says) not only has higher dps to begin with, this is effectively doubled when dodging versus Flareon. Short story is that Arcanine is still the strongest fire attacker. Thats said, against most vulnerable opponents (e.g. grasses) even Flareon will quickly cook them. But a really well powered up Arcanine is still the easiest way to power through a high CP Lapras.

Arcanine is still an attacking fire beast. I have a 95.6% Arcanine with Bite/Fire Blast and I don't ever think on stop powering him to max.

Still the best fire attacker as the other fellows said above. All pokemons that he was strong against got WEAKER and the ones that counters him got a lot stronger, but no one is stupid enough to attack a counter, even before.

To be honest i think that besides the CP nerf, he is even better now for the meta. '-'

Adding my vote of yes with the others. My Arc is still my go-to mon for Lapras and the grasses. It's still a beast, and I still plan on taking mine at least to level 30 (same strategy as before).