I agree with your speculation. I don’t think they’ll be launching the game in spring/summer, but do think they’ll reboot the marketing cycle for a Holiday 2021 launch.
There’s this sort of ever-optimistic feeling among the Halo community regarding Halo Infinite, despite the fact that feeling is entirely unwarranted, borderline delusional, and (not just unrealistic, but) “anti-realistic” (if you will). A lot of people are still holding out for a spring 2021 or summer 2021 release and I’m not here to say it can’t or won’t happen, but it’s just not being real about 343’s capabilities and where Infinite probably is.
A consistently brought up source is Klobrille, who’s currently talking up Infinite and it’s supposed status of being content complete; I just don’t buy it. Everyone has conveniently forgotten that Klobrille was the primary source of the reason behind the July Xbox event and Infinite reveal being regarded as bait-and-switch (if you trace all the hype back to the root, it was all the influencers sourcing Klobrille saying it was going to blow your mind and that Infinite had this graphical capability that would blow The Last of Us Part II out of the water and look truly next-gen). While Klobrille does have insider information, he definitely spins it (and sometimes in a big way) to keep the hype up for Microsoft.
And my point here isn’t that I’m 100% certain Infinite won’t launch in spring/summer, but that from what we’ve seen it’s heavily unrealistic and borderline delusional to believe so at this stage.
Another thing people keep saying is that this silence is just strategic planning by 343 to masterfully flank us with a launch and a wealth of new things to hype us up, and while I believe that it’s a strategic and intended silence, I don’t think it was necessarily “planned” (in the conventional sense) so much as “planned last minute to prevent further damage”. I believe the silence is strategic in the sense that they’ve done so to both hide Infinite and to (as you said) wait until 2021’s Holiday season to reboot their advertising cycle and launch the game. For some people it’s hard to believe that 343 isn’t really in control and just took a loss, but that really is the case- they seemingly don’t have a plan.
One might ask how I could make all these assertions about 343 when I don’t work there, but they’re missing the point: these are all speculations, theories, and beliefs drawn from making reason of 343’s actions and Infinite based on trends and patterns and such. Even if it’s the case that 343 does have a plan, that Klobrille is correct, and that there is a launch in spring/summer, it doesn’t appear that way right now, and that is a massive failure. Whatever the outcome of Infinite and the days ahead for it, it is massively losing as of current, and absolutely must be a success lest the dents and holes it has compounded on the Halo franchise be permanent and the whole ship sinks.