Sorry this took so long, had some stuff that came up but here is my response to this.
Here's a link to the feat so people can see it.
Alright so I want to start by saying I 100% agree with this upgrade and I will explain why below.
As stated in the OP, the 8-A / Multi-City Block level+ happens in the first episode of the series and Danny wasn't noticeably tired from preforming the feat. The Lunch Lady even asked him if he's ok and he responds saying he's fine, so this wasn't an all out attack. I'm also not saying it was casual either, just that it isn't his cap for the whole season which is proven over and over again.
Episode 1 "Mystery Meat"
This is were Danny preforms his Multi-City Block level+ feat.
Episode 4 "Attack of the Killer Garage Sale
In the episode, Danny encounters Technus, who was able to harm Danny. Technus the upgrades himself with technology from Danny's garage and an upgrade disc. Technus becomes so powerful that Danny couldn't even make him flinch with a barrage of punches. Danny then removes him from the Battlesuit 1.0 using the Fenton Thermos.
Why is this important you ask?. Because it is revealed in season 2 that Technus himself keeps the power that he had when inside the Battlesuits he creates which is why he got upgraded when he was removed from the Battlesuit 2.0 and could defeat Danny.
This means that the Technus Danny removed from the Battlesuit 1.0 is still just as strong as the Battlesuit itself, which means base Technus became strong enough to no sell 8-A+ Danny's blows and I want you to remember this because it is important.
Episode 6 "What you Want"
Tucker gains ghost powers and before he starts getting stronger, Danny admits Tucker is faster than him.
Tucker goes through two transformations and Danny became fast enough to keep up with him and yet him into the Fenton Dream Catcher.
Episode 11 "Fanning the Flames"
Danny fights Ember and the two are equal, then Ember gets a boost from the crowd chanting her name and overpowers Danny pretty easily.
After a few hours, Ember grows even more powerful thanks to countless people chanting her name around the world. However Danny's power increases in that amount of time to such a degree that they became equals and matched each other blow for blow.
This means Danny at this point can easily defeat his previous self no problem.
Episode 12 "Teacher of the Year"
Technus returns again and remember that he is at least as strong as he was before in his previous Battlesuit. He then makes a new Battlesuit and becomes stronger but this time, Danny was able to knock him down.
Technus then decideds to blow himself up and enter the Doomed video game and thanks to the mechanics of the game, he continued to grow in power and evolve. Danny also enters the game and like Technus, he kept his powers and is just as strong as he was outside of the game.
Danny thrn shows he could still effect the Technus who has become even stronger than he previously was in this very episode. This means Danny had become powerful enough to destroy his episode 6 self in a fight and take his blows with no damage...
Episode 13 "Fright Knight"
Danny battles the Fright Knight and literally is incapable of causing the later harm early on. After the fight a bit more, Danny grows strong enough to trade blows with the Fright Knight...
So this means Danny's power grew in a few minutes to the point were he could harm someone who previously could withstand his blows without even flinching.
Episode 19 "The Million Dollar Ghost"
Vlad stomps Danny again!. Then Jack amplifying his strength with the Ghost Gloves could damage and defeat that same Vlad...
Conclusion
Here's a list on how the stomps go down the line (this doesn't include everything, just the basics)
Vlad (End of season 1)
Stomps
Danny (End of season 1: Post Fright Knight fight)
Stomps
Danny (Episode 13: Pre-Fright Knight battle) / Technus (Data form)
Stronger than
Danny (Episode 11: Second Ember Fight) / Technus (Battlesuit 1.0)
Stomps
Danny (Episode 11: First Ember fight)
Stronger than
Danny (Episode 6: Pre Tucker fight)
At least as strong as
Danny (Episode 1: At least Multi-City Block level+)
Scaling
Throughout the season ghosts keep coming back stronger and stronger just like Danny be it though upgrades like Skulker and Technus or wishes like Desiree, or chanting like Ember. Almost every character reaches end season 1 Danny's strength so they would scale in the end. So we could just rate them at the end result since Multi-City Block level+ wasn't even Danny's maximum at that time, he and everyone else who continues to fight him come back stronger and I don't want more keys so I think it should be this.
Tier: Low 7-C
Attack Potency: Small Town level (
Caused this much destruction by smashing into the ground and has grown stronger over time. By the end of the season, he could match the Fright Knight who previously withstood his attack without even flinching)
Everyone else would have some variation to this since by the end of the season almost everyone was stronger than episode 1 Danny by a decent amount. Again, what I'm suggesting is just scale them to End Season 1 Danny so we don't need more keys.