What does Manetric outspeed that Raikou does not? Starmie, Tornadus, Hawlucha, Talonflame, Scarf ttar and modest scarfed Heatran. Out of these Raikou beats Starmie and Tornadus anyway and Hawlucha will outspeed both most of the time due to unburden. Manetric cant touch scarf ttar and loses to scarf heatran so its basicly just Talonflame where the speed gap realy matters. Add the tie with Lopunny if you want to. Sure Talon is an important thing to outspeed but that speed difference isnt as big as it might apear on first sight. Fire coverage doesnt hit anything relevant aside from Ferro and Scizor. In return Raikou has Shadow Ball for very good neutral coverage and also to hit all the psychics in the tier. Which gets us to Metagross:
252 SpA Mega Manectric Flamethrower vs. 0 HP / 4 SpD Mega Metagross: 186-220 (61.7 - 73%) -- guaranteed 2HKO
252 SpA Raikou Shadow Ball vs. 0 HP / 4 SpD Mega Metagross: 148-176 (49.1 - 58.4%) -- 97.7% chance to 2HKO
That's hardly even an advantage seeing that both of them 2hko most of time (always after SR).You could go for overheat but that leaves you wide open afterwards with that nasty -2 drop and isnt even a save ohko.
And against Latios for example it looks like this:
252 SpA Mega Manectric Hidden Power Ice vs. 0 HP / 4 SpD Latios: 124-148 (41.4 - 49.4%) -- 84.8% chance to 2HKO after Stealth Rock
252 SpA Raikou Shadow Ball vs. 0 HP / 4 SpD Latios: 148-176 (49.4 - 58.8%) -- 98.8% chance to 2HKO
Fire coverage certainly has its merits but your ignoring the extra coverage Raikou has in Shadow Ball or Extrasensory
On the fire coverage, I'm pretty sure Manectric prefers Overheat, since he's playing Pivot and won't be in long enough for the SpA drop to hinder him too much. Even then, having the option makes this just as if not more relevant
252 SpA Mega Manectric Overheat vs. 0 HP / 0 SpD Mega Metagross: 270-318 (89.7 - 105.6%) -- 37.5% chance to OHKO
Seems more an advantage now. Also, less common, but I have seen some EQ Metagross variants
-1 252 Atk Mega Metagross Earthquake vs. 0 HP / 4 Def Mega Manectric: 192-226 (68.3 - 80.4%) -- guaranteed 2HKO
252 Atk Mega Metagross Earthquake vs. 32 HP / 0 Def Raikou: 302-356 (91.7 - 108.2%) -- 50% chance to OHKO
There's another advantage for you.
Manectric outspeeding a lot of those mons is the most benefit he's going to need. Manectric's job is to weaken opponents and Pivot out with Volt Switch. A -1 ScarfTar is pretty exploitable, and if he outspeeds these mons, he switches out to an appropriate teammate anyway. Starmie does a number on Raikou in a lost Speed Tie
252 SpA Life Orb Starmie Psyshock vs. 0 HP / 0 Def Raikou: 181-214 (56.3 - 66.6%) -- guaranteed 2HKO
252 SpA Life Orb Starmie Hydro Pump vs. 0 HP / 32 SpD Assault Vest Raikou: 126-149 (39.2 - 46.4%) -- guaranteed 3HKO
56+39 = 95% minimum, without accounting for any Analytic switch boost on a mispredicted action.
Tornadus-T is carrying U-Turn most sets, so by outspeeding Raikou, he knows he's not the one getting hit, meaning Raikou doesn't necessarily beat him either. Manectric fares better since both check the opponent, but Manectric keeps momentum because Tornadus actually takes sizeable damage if he wants the slower Voltturn
252 SpA Mega Manectric Volt Switch vs. 132 HP / 0 SpD Assault Vest Tornadus-T: 170-204 (51.2 - 61.4%) -- guaranteed 2HKO
252 SpA Mega Manectric Volt Switch vs. 0 HP / 0- SpD Tornadus-T: 288-338 (96.3 - 113%) -- 75% chance to OHKO
Whereas, by outspeeding Raikou, Tornadus-T turns out, Regenerates, and brings in a Raikou check, possibly stopping Raikou from abusing the slower Volt Switch.
Of the Psychic types in the A-Ranks: Metagross, Lati@s, Celebi, Gardevoir, Slowbro, Starmie, Alakazam, Jirachi, Mew, Gallade.
Of these, the ones Raikou hits SE that Manectric doesn't: Gardevoir, Alakazam (Outspeeds both, KOs depending on Psychic vs Psyshock), Mew, Gallade.
232 SpA Mega Gardevoir Psyshock vs. 0 HP / 0 Def Raikou: 198-234 (61.6 - 72.8%) -- guaranteed 2HKO
232 SpA Pixilate Mega Gardevoir Hyper Voice vs. 32 HP / 0 SpD Raikou: 226-267 (68.6 - 81.1%) -- guaranteed 2HKO
252 SpA Raikou Shadow Ball vs. 0 HP / 0 SpD Mega Gardevoir: 124-148 (44.7 - 53.4%) -- 32% chance to 2HKO
252 SpA Choice Specs Raikou Shadow Ball vs. 0 HP / 0 SpD Mega Gardevoir: 186-220 (67.1 - 79.4%) -- guaranteed 2HKO
Raikou takes any hit entering (not just Psyshock, ANY hit) or comes with any particular prior damage, he loses. Neither handles her particularly well
Alakazam is in Raikou's favor, but still a shaky match-up
252 SpA Raikou Shadow Ball vs. 32 HP / 0 SpD Mega Alakazam: 168-198 (64.8 - 76.4%) -- guaranteed 2HKO
252 SpA Mega Manectric Thunderbolt vs. 252 HP / 0 SpD Mew: 153-180 (37.8 - 44.5%) -- guaranteed 3HKO after Leftovers recovery
252 SpA Raikou Shadow Ball vs. 252 HP / 0 SpD Mew: 160-190 (39.6 - 47%) -- guaranteed 3HKO after Leftovers recovery
Manectric hits about as hard
WITHOUT SE coverage. There's an undeniable power difference inherent to the two mons.
252 SpA Raikou Shadow Ball vs. 0 HP / 4 SpD Mega Gallade: 142-168 (51.2 - 60.6%) -- guaranteed 2HKO
252 SpA Mega Manectric Thunderbolt vs. 0 HP / 4 SpD Mega Gallade: 135-159 (48.7 - 57.4%) -- 94.1% chance to 2HKO
-1 252 Atk Mega Gallade Close Combat vs. 0 HP / 4 Def Mega Manectric: 189-223 (67.2 - 79.3%) -- guaranteed 2HKO
252 Atk Mega Gallade Close Combat vs. 0 HP / 0 Def Raikou: 298-352 (92.8 - 109.6%) -- 56.3% chance to OHKO
Both outspeed Gallade, but Manectric can survive the retaliatory strike to actually beat Gallade with a second T-bolt. Raikou often goes down after barely getting half off with Shadow Ball.
So of OU's Psychics, Raikou only handles Mega Alakazam noticeably better, so Shadow Ball isn't that big an advantage over Manectric's coverage.
You're also underselling the importance of checking Talonflame, considering Manectric is most effective as a Pivot for offensively oriented teams, teams that
REALLY hate Talonflame's Priority Brave Bird. While never breaking the S-Rank line, Talonflame has been nominated multiple times for a reason.
252 SpA Mega Manectric Volt Switch vs. 120 HP / 0 SpD Talonflame: 320-378 (97.8 - 115.5%) -- 81.3% chance to OHKO
Talonflame needs a SD boost to beat either w/ Flare Blitz, but unlike Manectric, SD Talonflame can afford to creep Raikou if it proves that much a problem. Assuming either enters on the SD.
Raikou: KO'd by Flare Blitz, Talonflame can potentially sweep with +2 Brave Bird
Manectric: Outspeed, Volt Switch KO's Talonflame (even the 20% of the time it lives, recoil finishes it). Talonflame leaves, Manectric stopped his sweep and got momentum. Talonflame stayed, opponent is out their Smog Bird.
Just because Raikou can KO the same targets, or that Manectric does not directly OHKO the things he outspeeds over Raikou, does not mean Manectric does not handle them significantly better.
The other thing to consider is limitation. Raikou can check a lot of Pokemon, but he's never going to be able to handle them all. Things he can handily check with the Specs set will murder him outright with the AV set, for example. Manectric only has the one set, but with that one set, I find he covers almost everything Raikou covers with combinations of his sets. So having Manectric on your team covers more than having a Raikou.
Truthfully, I always saw Raikou as one of those Pokemon that only just broke the B+/A- barrier, and I don't see him going to A unless some big shift happens that proves favorable to him and/or REALLY infavorable to Manectric.
Keep Raikou in A-