Here are my thoughts on chapter 246.
Go All Out and break you're arm
We get to see that Tomura Shigaraki did significant damage to his own body when he unleashed his Decay quirk against Re-Destro and the Meta Liberaton Army. Several parts of Shigaraki's arm appear to be missing layers of skin, the scars and cracks reach all the way up his arm to his kneck annd chest.
Dr. Ujiko exposits about how Tomura's quirk has evolved and asks Tomura why he seeks even more power.
"It's true...I have no more need for delicate moves. But I doubt this boost has made me unbeatable. Just ask CEO baldy he's still alive and kicking. And look at this arm. I went all out one time and this is what happened. How many of them are we going to face huh?"
I immediately drew a parallel between Tomura and Deku both destroying their arms after going all out with their quirks. They both have quirks that if used at their full power could hand them victory in nearly any fight at the cost of selff-mutilation There's a few reasons Tomura is much quicker to recognize the problem with relying on such power.
The first is that right now Tomura is more experience and mature than Deku was when Deku started breaking his limbs; if Tomura had awakened this ability back during the USJ arc he wouldn't have had such restraint. The second reason is that the first few times Deku hurt himself using OFA he won a complete victory and Recovery Girl healed all his wounds soon afterwards; so he got into a habit of thinking he could rely on this. A third possible reason is that Deku's heroic spirit and or specific psychological problems made him far more willing to self-sacrifice than Tomura.
Shigaraki is thinking tactically. There's a lot of heroes out there and victory probably wont be decided by just a single battle.
The dregs All Might left behind
"I'm done taking the heroes lightly. I'll use everything I've got to obliterate the dregs that All Might left behind....The next time we meet I'll finish them off."
I'm not exactly sure what Shigaraki is referring to here by "the dregs all Might left behind" there are a few different options and they aren't mutually exclusive. The first option is that Tomura is referring to Toshinori Yagi, the husk of a man that remains after the Symbol of Peace has been snuffed out. Tomura Shigaraki could just as easily be referring to Class1A or to the entirety of the Hero System.
Quirk Singularity Doomsday Theory
Dr. Ujiko taks to Tomura Shigaraki about Quirk Singularity Theory and how it relates to the power he craves.
"My research here...was originally intended for All for One. With each new generation quirks become more mixed....more complex...more ambiguous....more powerful....and more numerous. Even though our memory expands faster and faster, our hardware doesn't evolve quickly enough to keep up. There will eventually come a point when people lose control. I calll this concept The Quirk Singularity, Nobody except All for One ever took it seriously. Unless we can tweak the hardware to accomidate our expanding memory, the human race will become unsustainable. And since He held multiple quirks, he saw this problem as a grave one."
This isn't the first time the Quirk Singularity Doomsday Theory has been mentioned. It was mentioned by Seiji Shishikura back in chapter 166 in the "Remedial Course Arc". Later on during chapter 193 the First OFA user tells Deku "we've passed the point of singularity".