Mike Mearls has stated they designed the game around 6-8 combat encounters per adventuring day. I’ve quoted it. The Adventuring Day section clearly states that’s how things work.
That has nothing to do with the topic and I've never mentioned it in this thread.
The line about four PCs to one on-level monster is from another section of the DMG. Page 274.
“A single monster with a challenge rating equal to the adventurers' level is, by itself, a fair challenge for a group of four characters. If the monster is meant to be fought in pairs or groups, its expected challenge rating should be lower than the party's level. Don't fall into the trap of thinking that your monster must have a challenge rating equal to the level of the characters to be a worthy challenge. Keep in mind that monsters with a lower challenge rating can be a threat to higher-level characters when encountered in groups.”
I don't know where this quote is from, but DND Beyond cannot find it in not just the DMG, but in any 5e D&D book in it's database. I even cut up the quote into parts to try and find it that way, and nothing. It does not appear in the current 5e DMG as far as DND Beyond is concerned. The guidelines also never mention a party of four. They explain that the guidelines assume a party of 3-5, and give rules for less than three or more than five PCs, but never say four is assumed to be the standard and I did an extensive DND Beyond search for any variation I could think of on that phrase and never found it appearing.
Now maybe this was subject to errata and you never picked up the errata? I don't know. I just know none of that paragraph appears in the current official rules on DND Beyond.
Looking at the XP value of monsters compared to a medium encounter for a party of four…almost always yields exactly one on-level monster. You can break that up however you want, increase it, decrease it, etc. But the game is designed around 6-8 combat encounters per adventuring day and defaults to one on-level monster as a medium encounter. The DMG also explicitly warns about using monsters with a CR higher than the party’s level, especially for low-level PCs. The text is clear and the devs have explicitly said as much. If you refuse to acknowledge that, it’s your choice, of course.
I am, again, looking at the official text in DND Beyond for creating encounters and that is not how the formula works out. I can quote it for you if you don't have access?
Again, I never mentioned number of combat encounters and I don't know why you keep bringing it up? We were talking about how I think the game encourages groups of foes and you think the game encourages solo encounters. Neither of us had mentioned encounters per day.
To be clear. There’s a world of difference between what the default assumptions of the game are and how people actually play it. Me talking about the default assumptions isn’t me saying this is how I run it or how the DMs I’ve played with run it.
See above.
No, as I said, some monsters do, some don’t. If the monster is trying to kill the PCs and is smart enough to realize what’s going on, then they double tap. But it’s not the default for all monsters all the time in all situations.
Why would an animal not try to kill the thing it just knocked down that was hurting it? Why would the foe have to be more intelligent to kill its prey? I was using as an example Tomb of Annihilation and that adventure has lots of undead and dinosaurs. Both tend to want to kill the things they knock down, either because the description says they want to snuff out life (undead) or they are carnivores attacking prey (a T-Rex). In either case, their opponent being knocked unconscious doesn't seem like it would be the end of their attacks on that target. Particularly in the few seconds of their round. If a dinosaur claws you and you go down, they will still tend to claw and then bite your still breathing form that's right in front of them because you pissed them off and are squishy and vulnerable to their claws and bite.
It sounds like your DM is just trying to spare your PCs?