Well, the point here should be that weapons allow the user to draw out power. Power which also works physically. I mean, why else would the sins have trouble with guila or jericho?
But their speed? I don't buy that. Weapons focusing their magic and strength (in terms of using the weapon), I'll buy, but speed shouldn't be affected. The Sins could have had trouble with Guila and Jericho because the plot demanded it. Going by that fight in Byzel, Guila and Jericho were on the level of Gilthunder. But, earlier in the series, we saw that Mel was easily able to outmaneuver Gilthunder without any weapon.
It seems like even if the sins did not have weapons their sheer physical capacity should have been enough to overwhelm them. I mean, the sins seem to have at least over 3 times the PL of guila and jericho. The sins have power upward of 3000 and guila and jericho have power between 500 (average HK power if we consider their amount and cumulative pl) and 1300 (the power of red demons). In turn guila and jericho overpowered the sins even physically. Meliodas had trouble even getting close. However once the sins started getting weapons and using them they never lost a physical confrontation. If anything meliodas with an inferior weapon was stronger than gilthunder, hendrickson and vivian. They could not even match up to him from a physical point of view...
If just having a weapon pulls out all aspect of physical power, do you believe it also increases durability? Because Mel has taken much worse damage than what Guila dished out in her earlier appearances and gotten right up afterwards, unlike his fight with Guila where he'd seem tired and/or injured.
I also think Balor's Eye muddies this discussion up a bit. For example, from what we've seen, Gilthunder, Hauser, and Griamor as individuals had more than enough power to fodderize a Red Demon without assitance, but earlier in the series, we saw Ban fight a Red Demon and he had more trouble with it than his power level would indicate. I think the author just made the Sins stronger period as the manga went by.
Meliodas did activate his sacred treasure but that seemed to be related to his clone ability. The speed which was referenced does not make sense with the clones being activated. Unless 5 simultaneous cuts that appear because of the clones were initially confused for speed of course. Cutting the albion seems to be more of a merit of Mel's sacred treasure rather than the increase in power. Basically its inherent sharpness did the did. If it was power alone then king with chastiefol should have been able to turn albion into confetti since king's PL was higher than mel's. In turn it did not seem like king's cutting attacks had much of an effect even though they should have had more power than mel's basic attacks. To add to that, even the clones were able to cut the albuon even though their power is at around the 300 mark or so.
Well, assuming Lostvayne is vastly sharper than Liz's Blade, the cutting part makes sense. As for the speed, I figured it had to do something with the clones because of Arthur's comment and Mel's activation of Lostvayne. Another take could be that Mel had been careful with Liz's Blade and never really went all out with it, but because Lostvayne is of a higher quality, it can take what he can dish out. Another possiblity and that Mel can temporarily add on the stats of his physical clones for power, but that's a bit out there. I don't know. As for King, it seems to be an ongoing thing that his weapon has a problem piercing certain things. It had an issue piercing Dale's hide a while back as well. It's strength lies mostly in it's versatility, rather than it's outright killing potential.
---------- Post added at 01:46 PM ---------- Previous post was at 01:21 PM ----------
I think you're exaggerating a bit but really, it's your word against this conspicuous manga statement "So this is the power of the sacred treasure...! No' this is the true power of one of the seven Sins being drawn out by the sacred treasure".
But that could be, and is most likely, in reference to the magical aspect of the Sins. In fact, it's already been recently explained that Sacred Treasures are given to the Sins because it goes well with their unique magical ability. Lostvayne is "useless", so to speak, in the hands of other folks aside from Mel because all they'll get is weaker clones. In the hands of Mel, it allows him to maximize Full Counter's reflective ability. It doesn't increase his physical strength (as far as I'm aware of), it doesn't increase his spirit, it completely compliments his unique magical ability. When Helbram made that statement, Diane's demonstrated an increase in effectiveness, power, and range in her use of Creation, not anything else. Every attack she's shown with Gideon since then, have been attacks used in conjunction with Creation. Except that time she got clocked in the face by Galan.
