Magneton; Laurantis; Inceniroar oh my!
I'll be blunt about the Litten line. It actually sucks. Until Litten evolved at lv 34 it's best move was Fire Fang. Even now it's slow as molasses and has quite a lot of weaknesses and honestly feels carried by the absolutely insane boost Lariat gets from the Incenium Z.
Oh; and Popplio gets a stupidly early TM Scald; while Rowlet gets Grass Knot early and Shadow Ball not too far from when it's evolving. Litten; meanwhile? Either I've missed a ton of TM's or it dosen't get any useful ones for ages. My Inceniroar still knows Scratch and Lick. That's how bad it's movepool is. I mean I guess you can patch up the speed a bit with Flame Charge; but then you're either running an even weaker fire move or doubleing up on fire moves...
Litten even got screwed on it's exclusive Z-Move... it only gets a +95 BP boost to 180; while Arrow Raid is a +100 [80->180] and Primarina gets a +105 [90->195. Why does the strongest move to start with in terms of BP get the biggest boost? Why does Primarina get a BP195 while the others get 180? Oh; and Primarina's Z-Move can benefit from Torrent. Deducieye's and Inceniroar's can't benefit from Overgrow/Blaze.].
I think this might be the first time that the Fire-type starter is hands down the worst one other than Charmander... and Charmander certainly isn't the worst these days with MegaZards.
And maybe Tepig. But all the Gen 5 starters sucked in-game and were outclassed so ity's kinda hard to call if Tepig or Snivy were worse in-game.
To be fair, all three Gen 7 starters are fairly slow, which is a theme for a bunch of Alola's Pokemon in general.
Obviously I can't say anything regarding playing through with the other two starters, but Incineroar definitely felt far from useless. You get Bulk Up and Leech Life on the second island, which can provide it with some extra longevity (beyond your own healing items lol), and Incineroar itself has decent natural bulk to help that out (less so before it evolves, however). Fire is well known to be terrible defensively, so that's something you just kinda have to accept going into it - at least Fire is also really good offensively, unlike Grass. Admittedly I didn't find too many situations in-game where Darkest Lariat's secondary effects mattered (competitive players are more privy to using boosting moves than CPU opponents), but then again, I doubt Decidueye or Primarina can say anything better about their signature moves' effects in-game (very few CPU trainers switch their Pokemon at all, and why would you ever want to heal an opponent's burn in singles?). Even before evolving, Torracat is by far the fastest of any of the starters' forms, which has to count for something. So yeah, while I can agree that Primarina's typing and movepool are better just from a glance, I wouldn't say Incineroar is, say, vastly inferior to Decidueye for the purposes of going through the campaign.
And Sparkling Aria's Z-move is stronger because its base power is in a higher increment of 10, which is generally how the Z-moves' base powers are determined. For example, Flamethrower and Heat Wave have base powers in the 90s, so an Inferno Overdrive from both is 175 base power despite the original moves' power difference (90 vs. 95), while one from Sacred Fire (100 base power) gets bumped up to 180 base power. The starters' signature moves work similarly, i.e., original moves with base powers in the 80s vs. the 90s.
