I'll defend the case for the fity's defensive tirtouga though since that seems to have potential.
196 Atk Life Orb Aipom Knock Off (97.5 BP) vs. 92 HP / 252 Def Eviolite Tirtouga: 6-8 (26 - 34.7%) -- 0% chance to 3HKO
(6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 8)
196 Atk Life Orb Aipom Brick Break vs. 92 HP / 252 Def Eviolite Solid Rock Tirtouga: 8-10 (34.7 - 43.4%) -- guaranteed 3HKO
(8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 10)
196 Atk Life Orb Aipom Brick Break vs. 92 HP / 252 Def Solid Rock Tirtouga: 10-12 (43.4 - 52.1%) -- 0.4% chance to 2HKO
(10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 12)
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0 Atk Tirtouga Stone Edge vs. 76 HP / 0 Def Aipom: 13-16 (56.5 - 69.5%) -- guaranteed 2HKO
(13, 13, 13, 13, 13, 13, 15, 15, 15, 15, 15, 15, 15, 15, 15, 16)
0 Atk Tirtouga Aqua Jet vs. 76 HP / 0 Def Aipom: 6-7 (26 - 30.4%) -- guaranteed 4HKO
(6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7)
Coming in on rocks tirtouga takes 2 damage to bring it to 21 health. The most damage aipom could do to it is 20 with two max damage brick breaks. Tirtouga would survive on at least 1 hitpoints and if it can land a stone edge with an aqua jet to follow it up it could do at least 19 damage. This aipom has 23 health. HOWEVER, it would lose 4 health in recoil from the two attacks it used attack tirouga which would bring aipom down to 19 health and in range for tirtogua to kill it.
I would say that defensive tirtouga can counter this aipom IF stonedge connects and aipom doesn't get a crit. There is some luck here. I don't need to do the calcs for archen since Rowan already did them. It does appear to be just as viable of a counter as tirouga I would say since the probability of getting those max damage rolls is very low. Both archen and tirouga need a little luck here to avoid crits, land hits, and avoid max damage rolls, but both have strong potential to counter. I will say, however, that IMO defensive archen is less commonly used compared to defensive tirtouga.