What if I told you there was a mon that could switch into mega-mawile, magearna, tapu bulu, tapu koko, and tapu lele? A mon that could reliably set rocks, block volt switch, and one v. one kyurem-black, zygarde, heatran, lando-t, garchomp, and toxapex? All this mon costs you is wish support, and an open mind.
I present:
Mega-Steelix for C-
View attachment 146774
Steelix with Steelixite
248 hp 152atk 108 spdef adamant nature
Stealth rock
Heavy slam
Earthquake
Ice Fang/Roar/dragon tail
I'm going to go through select matchups. It should be obvious this thing beats bulu and koko, lele locked into not focus blast and magearna lacking fightinium z.
Matchup with Mega-Maw
Offense: 152+ Atk Steelix-Mega Earthquake vs. 40 HP / 0 Def Mawile-Mega: 270-318 (107.5 - 126.6%) -- guaranteed OHKO
Defense: +2 252+ Atk Huge Power Mawile-Mega Fire Fang vs. 248 HP / 0 Def Steelix-Mega: 256-302 (72.5 - 85.5%) -- guaranteed 2HKO
+2 252+ Atk Huge Power Mawile-Mega Knock Off vs. 248 HP / 0 Def Steelix-Mega: 128-151 (36.2 - 42.7%) -- guaranteed 3HKO
Aggron: 252+ Atk Aggron-Mega Earthquake vs. 40 HP / 0 Def Mawile-Mega: 210-248 (83.6 - 98.8%) -- guaranteed 2HKO
40 Atk Aggron-Mega Earthquake vs. 40 HP / 0 Def Mawile-Mega: 164-194 (65.3 - 77.2%) -- guaranteed 2HKO
Commentary: Steelix eats any mega-mawile attack on the switch or at +2 bar the rare brick break and focus punch. Unlike main competitor aggron, stab earthquake guarantees ohko while still being able to invest in special defense.
Matchup with Kyurem Black
Offense: 152+ Atk Steelix-Mega Heavy Slam (60 BP) vs. 0 HP / 0 Def Kyurem-Black: 198-234 (50.6 - 59.8%) -- guaranteed 2HKO
Defense: 4 SpA Teravolt Kyurem-Black Earth Power vs. 248 HP / 108 SpD Steelix-Mega: 142-168 (40.2 - 47.5%) -- guaranteed 3HKO
252 Atk Teravolt Kyurem-Black Subzero Slammer vs. 248 HP / 0 Def Steelix-Mega: 190-225 (53.8 - 63.7%) -- guaranteed 2HKO
Aggron: 252+ Atk Aggron-Mega Heavy Slam (40 BP) vs. 0 HP / 0 Def Kyurem-Black: 152-182 (38.8 - 46.5%) -- guaranteed 3HKO
40 Atk Aggron-Mega Heavy Slam (40 BP) vs. 0 HP / 0 Def Kyurem-Black: 120-144 (30.6 - 36.8%) -- 61.4% chance to 3HKO
4 SpA Teravolt Kyurem-Black Earth Power vs. 248 HP / 0 SpD Filter Aggron-Mega: 136-162 (39.6 - 47.2%) -- guaranteed 3HKO
Commentary: Steelix doesn't hard counter kyurem as it fears subzero slammer, but with the listed evs 2HKOes Heavy Slam while not being 2hkoed by any non-z move. Here again the comparison with aggron shows the benefits of being able to invest in both atk and special defense. Offensive aggron can't 2HKO Kyurem while not taking earth power any better than steelix. Finch's spread isn't even guarantueed to 3HKO kyurem-black. It should be noted neither aggron outdamages roost while steelix does. As such despite not being able to switch into subzero slammer Mega Steelix is actually a better answer to Kyu-B since it can actually you know threaten back.
Matchup with Heatran
Offense: 152+ Atk Steelix-Mega Earthquake vs. 0 HP / 0 Def Heatran: 616-732 (190.7 - 226.6%) -- guaranteed OHKO
Defense: 252 SpA Heatran Magma Storm vs. 248 HP / 108 SpD Steelix-Mega: 306-362 (74.6 - 92.5%) -- Guarantueed 2HKO
Commentary: Obviously Steelix should never switch into heatran, but if your opponent brings in heatran against you on say a predicted stealth rock you can stay in and kill it unless they go for inferno overdrive (which they probably won't do if you have a good fire switchin, which you need). Depending on the matchup, this can be advantageous if say they need tran more than you need steelix. This is a matchup where Steelix truly is ouclassed by aggron as the added power to earthquake isn't needed and aggron takes less damage.
Matchup with ground types (grouped together)
Offense: 152+ Atk Steelix-Mega Ice Fang vs. 188 HP / 0 Def Zygarde: 240-284 (59.4 - 70.2%) -- guaranteed 2HKO after Leftovers recovery
152+ Atk Steelix-Mega Ice Fang vs. 4 HP / 0 Def Zygarde: 240-284 (67 - 79.3%) -- guaranteed 2HKO
-1 152+ Atk Steelix-Mega Ice Fang vs. 80 HP / 84 Def Landorus-Therian: 188-224 (55.4 - 66%) -- guaranteed 2HKO
-1 152+ Atk Steelix-Mega Ice Fang vs. 252 HP / 240+ Def Landorus-Therian: 148-176 (38.7 - 46%) -- guaranteed 3HKO after Leftovers recovery
152+ Atk Steelix-Mega Ice Fang vs. 4 HP / 0 Def Garchomp: 296-352 (82.6 - 98.3%) -- guaranteed 2HKO
Defense: 252 Atk Garchomp Earthquake vs. 248 HP / 0 Def Steelix-Mega: 156-186 (44.1 - 52.6%) -- 18% chance to 2HKO
252+ Atk Choice Band Zygarde Thousand Arrows vs. 248 HP / 0 Def Steelix-Mega: 192-228 (54.3 - 64.5%) -- guaranteed 2HKO
0 Atk Landorus-Therian Earthquake vs. 248 HP / 0 Def Steelix-Mega: 144-170 (40.7 - 48.1%) -- guaranteed 3HKO
148 Atk Landorus-Therian Earthquake vs. 248 HP / 0 Def Steelix-Mega: 158-188 (44.7 - 53.2%) -- 27.7% chance to 2HKO
Commentary: Steelix beats all these mons on the switch or if they click anything other than earthquake. Obviously steelix should not be switching into them but it doesn't fear earthquake. I won't show aggron calcs here but suffice to say offensive performs a bit better than steelix taking less damage with filter and hitting a bit harder with ice punch. Finch's set loses to all these mons without ice coverage.
Matchup with The Pex
Offense: 152+ Atk Steelix-Mega Earthquake vs. 248 HP / 8 Def Toxapex: 224-266 (73.9 - 87.7%) -- guaranteed 2HKO after Black Sludge recover
Defense: 0 SpA Toxapex Scald vs. 248 HP / 108 SpD Steelix-Mega: 98-116 (27.7 - 32.8%) -- guaranteed 4HKO
Aggron: 40 Atk Aggron-Mega Earthquake vs. 248 HP / 8 Def Toxapex: 138-164 (45.5 - 54.1%) -- 3.9% chance to 2HKO after Black Sludge recovery
252 Atk Aggron-Mega Earthquake vs. 248 HP / 8 Def Toxapex: 160-190 (52.8 - 62.7%) -- 99.6% chance to 2HKO after Black Sludge recovery
Commentary: Here is where stab-quake shows its muscle. Steelix hits defensive mons like toxapex much harder than aggron, and can actually kill the damn thing which bulky aggron can't do.
Replays: I'm using replays from Cookeez Anti-Meta team which peaked at 2017, I've used mega-steelix myself but only to like mid 1700s, so his opponent quality is quite a bit better
https://replay.pokemonshowdown.com/gen7ou-772557562
https://replay.pokemonshowdown.com/gen7ou-773279548
https://replay.pokemonshowdown.com/gen7ou-772155766
https://replay.pokemonshowdown.com/gen7ou-772557562
Closing arguments:
I think mega-aggron has demonstrated the value of a mega bulky physical steel type and they mostly do the same things. Set rocks counter some of the hardest hitters in the tier. The question is can they both be ranked. I think so because a) Steelix differentiates itself from Aggron with its ground typing and b) Steelix is in my opinion better than Aggron. Steelix's distinction over aggron is being able to block volt switch from mage, and shit on tapu koko. Also stab quake hits a lot harder than any of Aggron's sets, while the extra poundage ups heavy slam in some matches. This allows Steelix along with its superior special defense stat to run an optimized build that allows it to take super effective special hits as well as offensively EVed aggron while hitting much harder than finch's specially defensive aggron. Last but certainly not least Steelix's normal form takes damage much better than normal aggron making it easier to get into the battle and removing the need to lead with protect. In conclusion, rank the big worm its not outclassed.