Actually, there are a few things that point to ARMS not being intended as the first character. They revealed it without a trailer and without the character, the actual reveal is in June and maybe June was the only intended reveal. The march semi-reveal wasn't necessary if there was another character supposed to be revealed at that time, and that reveal clearly looked low-effort as if it was not prepared. Besides, they didn't clarified the release of the ARMS character, so it could be even later. For the first FP2 character to be revealed 6-months after the last FP1 character, it's a strange timing when we know they should release about 3 characters per year.
On the other hand, it's totally possible that Corona just delayed the development of the ARMS character. But honestly, I work as a developper and the situation didn't really delayed our work. It's very easy for developers to work from home. There are a few things like voice acting that could be more complicated though.
I went back to double check, and in the ARMS teaser they said the fighter "will be revealed and released in June."
We know from one of Sakurai's tweets to Japanese FP1 buyers from back in winter 2018-19 that for the first FP three characters were in development concurrently (I assume at varying paces, but there's no way to know). Sakurai has also said that it take about 6 months to finish a character (this is from memory, I couldn't track down the source it comes from). However, right from the beginning and before Corona FP2 was slated to release by the end of 2021. 6 characters over 24 months is way slower than the 5 characters over 15 months of the first FP. While some of that is probably due to reduced staff, it could be they've reduced production to 2 fighters at a time <--
THIS IS PURE CONJECTURE
So...
let's say the ARMS fighter started development after Terry's release in late November/early December. This would be appropriate if the ARMS fighter were the first in a two character rotation or the second in a three character rotation. If we keep a six month turnaround time, that would put the release some time in May. tbh, I could see a slightly scaled back team extending that time to June, and it does explain why there wasn't anything to show off in March.
BUT if things were still going on schedule anyway, and they were intent on a simultaneous full reveal and release, then the only reason they would have for the teaser at all (aside from a behind the scenes shuffle, which I will get to) is to sate all the smash fans online asking "who's the next fighter?" which seems distinctly unlike Nintendo to me. They play their cards very close to their chest, even when what their hiding is super obvious.
If instead, the ARMS rep began development after Banjo in September, a 6 month dev cycle puts an appropriate release mid-March. If
that's the case, it makes way more sense that Nintendo would make a big deal about publicly confirming some detail of the fighter in development, because at that point they're genuinely behind schedule. And sure, the Corona situation played a part, but even in the teaser they make mention that the complexity of an ARMS fighter is the main cause of the delay.
The scenario of the character swap, to me at least, would have to go something like this:
-Character 1 (let's say Reimu) enters development in September
-The ARMS fighter enters development in December
-By March, progress on Reimu has slowed so much that it makes more sense to switch over to the ARMS rep
-Because of the delay, Nintendo gets out ahead of the drought and says an ARMS char is coming
-the ARMS fighter releases in June, followed by Reimu in August/September
With so little information to work with, it is hard to piece together what is really going on behind the scenes. But with what we do know, I'm not seeing enough to say that there was a swap. I think that the second scenario presented makes the most sense, and that we can take Nintendo's statement at face value that the ARMS's characters development was delayed in part because of design difficulties.
