I personally don't think the pandemic really did anything huge to the 2nd Pass' development. If it did it was very minimal, as they have said a few times that they have been on schedule despite having to work from home.
We know for a fact that they develop batches of 3 characters at the same time (we know this from Sakurai himself), and seeing how Sephiroth took less than two months to reveal and release after Steve, is proof enough that they've been indeed on schedule from the start, and that Sephiroth was always gonna be at TGA and not earlier. He was the big reveal in a gaming event.
Steve was probably always gonna be revealed after E3 as well, the guy took the team effort of reworking / readjusting all the stages and its freaking variants for his gameplay gimmick to work on them. It makes sense that he took multiple months to be revealed after Min Min. Would he have been still revealed early alongside Min Min in a hypothetical E3 in 2020? Hard to say, considering he was revealed in the same week as Minecon, I think there's a chance that he was scheduled to be ready for Minecon to make a highlight of his inclusion in Smash, which they did highlight.
Min Min full reveal and release was in June, but I think many people are assuming she would've happened earlier if it wasn't for the pandemic, because people have this idea that Pass 2 was going to start right away a couple months later after Pass 1 ended with Byleth……… I don't know where people got this idea, but whatever… I'm just saying, maybe it was always the plan to start Pass 2 a few months later than usual to give themselves a little break after Pass 1?
I don't think they ever intended starting Pass 2 right away after Byleth. You gotta keep in mind that the pandemic didn't hit Japan hard until mid April 2020, which by that point Min Min has been in development for a while already. Would she have been revealed and released prior to the hypothetical 2020 E3? Maybe, but not so much earlier when you remember how the pandemic didn't really start affecting them until mid April, which at that point June wasn't far away. Again, they said they were on schedule with pass 2, several times, and the fact that Steve was ready before Minecon, and Sephiroth by The Game Awards, is enough proof of that, in my opinion. And Pyra also didn't take longer than 2 months after Sephiroth, to be revealed, so yeah… they clearly have had a nice pace on releases of DLC fighters of Pass 2 despite the Pandemic. I don't think we were ever gonna get 2 reveals in June 2020. The reveals happened as and when they intended them to.
It was more due to the timing of the start of the pass and how they scheduled the first half of the pass to happen. We are perfectly in time to get a new reveal in June, which is further proof that they have really been always on schedule, despite not having more than one ready in June 2020.
So the big question… Will they do 2 or 1 reveal?…
There are 2 ways this can go:
a) They do 1 reveal only at E3, because there is no reason nor pressure or hurry to reveal 2 huge characters anymore, we already got the 2 huge characters of Pass 2, their names are Steve and Sephiroth and they happened in positions of the pass similar to how and when big reveals of base game and Pass 1 went.
b) They do 2 reveals, not because we are ending on a high note, because we are not, lol… But because they might make this E3 direct similar to the one we had earlier this year, which covered the first half of 2021 announcements and releases. So they might just make a similar direct where they just cover all of the things happening on the second half of 2021, including the Smash reveals.
It's a 50/50 situation if you ask me, both ways are just as likely imo.
But hey, that's just me and how I analyzed the situation based on some facts. Feel free to disagree, lol.