-They don't need to be love interests. They could be thieves/mercs that DD has to deal with.
But DD has lots of characters that fill that niche, half of his rogues gallery are mercenaries and he even has guys like Paladin, who was a gray merc character before Silver Sable existed. I don't think Black Cat pr Silver Sable are essential or bring anything to the table that other DD related characters don't bring themselves. I won't complain if they appear, but I would rather have the focus be on characters from the DD mythos first.
-I don't find Mr. Fear to be nearly as interesting as Mysterio TBH.
That's debatable, after that Brubaker story, I would say Mr. Fear is far more evil then Mysterio is, Mr. Fear is a serial rapist and mass murderer at this point, his hatred of Matt Murdock seems far more intense then Mysterio's. Mysterio's motives were too convoluted in that story to work in a more streamlined setting. Mr. Fear has more of a defined history with Murdock, they went to same university, where Mr. Fear developed a jealous hatred of Murdock.
In Guardian Devil, Mysterio got cancer from inhaling smoke and chemicals during his super villain career (which wouldn't make sense if Mysterio has not been around for decades, which he wouldn't be in the MCU), he wants to go out with a blaze of glory, so he targeted Spidey for his grand finale, but changes his plans when he discovers Spidey was a clone (this was shortly after the Clone Saga) and switched his target to DD instead. Then at the end he kills himself. All of that doesn't work in a more streamlined, self contained contuinity like this show, Mr. Fear just has simpler reason for hating Murdock then Mysterio, that requires less explanation and do you really want Mysterio to kill himself during his first appearance in the MCU?
-So what? They're using The Owl as a crime boss already it appears. So how would Tombstone be any different?
Well in the Daredevil comics Kingpin and Owl serve different roles, Kingpin is the cool, confident, in control crime boss that thinks 10 steps ahead, Owl is a violent, impulsive psycho who is very short sighted and kills at even the hint of a slight. So you can contrast the two of them. What role would Tombstone play that would different from that as a crime boss?
No one is talking about shoehorning in a ton of Spidey stuff. But using SOME of it, why not? You have all of these "street-level" characters operating out of the same damn city. Frankly it'd be more disappointing NOT to see them interact.
Well I think with fewer characters, you can tell a tighter, more cohesive story, then trying to throw in every Marvel street level character and their brother in all at once. I would rather this show not become a "freak of the week" type show, more focus on a smaller cast would allow for a more involved story. The first season seems to be keeping a pretty tight focus on a small number villains, the only major villains seem to be Owl and Kingpin, Bullseye and Elektra are not in the first season. I think putting in too many characters at once would make the story lose focus, especially if they are not relevant to the main plot.
Also this is Daredevil's show, I think his villains and support cast should get priority over other street level characters. I don't mind some Spidey characters appearing down the line, but I think the focus should remain on Daredevil and characters from his mythos.