Base Pikachu was already seen to be more powerful than any Ash's Pokemon except A-G. As of Gigachu he's been more powerful than Base Zard but so was A-G (Base Gardevoir).
Hmm, considering that Diantha wasn't battling 100% all-out vs A-G (though A-G did overpower Mega Gardevoir's multi-fused Shadow Ball and was able to inflict serious damage, which indicated that A-G definitely was capable of taking on Base Gard in a serious fight) and Leon battled Ash in a 100% serious fight (since he's straight up accepted a challenge from Ash), I'd say that Gigachu deserves more credit. Further considering the fact that Leon is a World Champion who managed to straight up defeat a champion in Lance with less than extreme difficulty (while Charizard vs Gyarados was a close battle it still definitely wasn't down to the wire), he is above Champion level in general, while elevates Gigachu's feat even more. I'd say Gigachu probably is around MCX level or maybe even high.
We have seen that Base attacks don't work on Gigachu, but that doesn't mean Mega, Z and A-G attacks don't work. We need more feats from Gigachu at least to see how powerful it is. A-G is super speedy which would evade attacks from Gigamons(seeing how Giga can also evade them).
Agreed with the statement that he needs more consistent feats to establish its strength and power level, though if we had to scale from the Leon battle, then IMO Gigachu deserves to be put on a level which is definite cut above A-G. Though yeah, unlike many other Base Pokemon, attacks from high-level ME Pokemon or A-G would probably affect Gigachu.
Question for you which I already asked before: SM Peakachu with 10MV attack( vs Tapu Koko) would it beat Gigachu?
Gigachu, even though SM Peakachu with 10 MVT would put up a really close fight I'd assume. Pikachu's win vs Tapu Koko shouldn't be underestimated because it had to overcome Guardian Of Alola Z-move to win there; I mean that all the 3 other Tapu's gave their energy to Tapu Koko and Guardian Of Alola was used via that combined power/energy, so Pikachu (with 10 MVT) basically had to overcome the power of 4 Tapus combined to defeat Tapu Koko in that battle. It's one thing to just defeat a Tapu 1 on 1, and another thing to defeat a Tapu via overcoming its Z-move.which was used by the combined power of 4 Tapus. So yeah, Pikachu's feat vs Tapu Koko can probably be termed as the 2nd best feat after the Gigachu feat vs Leon IMO.
Also where do you see Ash's SM team in regard of power? I made several statements that Incineroar surpassed Snorlax but not that much. Naganadal is kinda featless(it beat Lucario who get defeated by Guzzlord easily and lost to TK), but question is Melmetal, Rowlet and Lycanroc(Rowlet is weakest).
Hmm, to be fairly honest, most of the Kukui battle was pretty much messed up power-scaling wise. The writers wanted to structure the battle in a way that most of Ash's Pokemon got a win there and for the sake of doing so ended up creating several logical holes characterized by power inconsistencies in that battle which are very hard to miss (which by an extension, goes to show that the whole battle wasn't thought out that well). We saw Pikachu struggling against Kukui's Empoleon enough to be recalled back and then eventually going toe to toe with Tapu Koko (which does indeed look like a glaring inconsistent portrayal of Pikachu in that battle), we saw Lycanroc being capable enough to give trouble to Kukui's Incineroar and then lose fairly decisively to Braviary afterwards (even though Braviary was shown to be relatively fodder compared to Incineroar back in the Neczroma arc, when Braviary alongside Faba's Pokemon got curbstomped in an instant by Gozu's Mega Aggron and Incineroar with Z-move destroyed Mega Aggron with little to no effort afterwards), all these inconsistent portrayals of power levels of the Pokemon involved in the battle several times makes it quite a bit tricky to scale and gauge the power levels of Ash's Pokemon from that battle TBH.
But well, if I had to make a good enough estimate I'd say that Incineroar, as of the Kukui battle and as Torracat with Z-move (since we never got to see it battle as Incineroar we can't properly gauge what its power level was as Incineroar) is a bit above Snorlax level but not by much. As Incineroar, taking the evolutionary boost into account, via estimate it could potentially/plausibly be on Sceptile/Infernape level though we can't say anything about that unless we see it battle as Incineroar.
Judging Melmetal & Lycanroc's power level as very tricky because of the power inconsistencies in the Kukui battle which I already explained above, but I had to make an estimate Lycanroc is still within the Tier 2 range of Ash's Pokemon (below the likes of Her across, Krookodile, Gliscor but around Swellow level or maybe even below) because while it did deliver the remarkable historical moment of Ash winning a League via getting the final & decisive victory against Gladion, we gotta be realistic, that feat has more landmark significance rather than being a strong feat in terms of power. Even then, from the battle it was kinda evident that Midnight was the superior Pokemon in terms of battle viability overall, but Ash's superior, situational & clever usage of Counter won Dusk the battle. The loss against Braviary still hurts it pretty bad I'm afraid, hard to put it higher after that loss.
Melmetal's best feat still is putting up a solid fight against Gladion's Silvally. Empoleon was a good win and all (though the power inconsistencies in that battle especially as pretty obvious in the Empoleon part, makes the feat very hard to take seriously & gauge anything from it) but it was still defeated quite easily by Incineroar without much fuss. I won't be too harsh on Melmetal for that loss though since it had severe disadvantage there, it's always hard for a Steel type Pokemon of that size and low speed to fight an OP Fire type Pokemon who knows Blast Burn. I'd put it around the level of Heracross, Gliscor & Krookodile.
For Naganadel, I'd say that it's probably a bit below Melmetal or around that level. It probably does deserve some credit because it did manage to hold out against Tapu Koko for a while even after being weakened a lot by fighting Lucario beforehand (further considering the fact that it had to face a severe disadvantage in fighting a Steel type), so yeah, even though it seems kinda DEM-y for a Pokemon who got released as Poipole with zero battle experience to become that strong upon return, it deserves to be put around the same level as Melmetal or maybe a bit below.
For Rowlet, while it may look weak and be a comic relief most of the times or whatever, it still performed consistently in battles and did its bit. Beat a fully evolved Pokemon of its own evolutionary line which is never easy (yeah I'm well aware of whatever BS was involved in that battle, but Rowlet still did win legitimately, because it wasn't it's fault that Nanu mistook its sleeping as fainting), beat a moderately damaged Braviary who defeated Lycanroc.....so yeah, I think that while it's the weakest amongst Ash's Alolan team, it still does hold a respectable place amongst Ash's flyers, definitely above the overrated Staraptor.
That basically sums up my overall views.