Well, I read an errant Twitter in the morning where a PG employee boasted about they could now show what they had been working for the past 2 years. So the 2 year development cycle is back, apparently, and maybe the improved sounds are part of that.
By my calculations and guesswork, this will have been the longest dev time a Horizon has had since the first game (if not longer)
Pre-Production for FH5 probably started just before FH4 shipped (a small team of department heads most likely) and they would've been concepting ideas, locations etc. Then as FH4 shipped, slowly more of the teams would've moved over to the FH5 team.
Once both expansions had been complete (so probably late May/June 2019), pretty much all of the FH4 Forza team would've moved over to FH5, barring a small live service team (the same team that has been bringing Series updates to FH4). On top of this, PG have been hiring like mad for both the Forza and Fable teams, so both teams have been expanding too.
So full production of FH5 would've started around May/June 2019, with the concepting, pre-production etc already done. By the time FH5 releases on November 9th 2021, it will have been 29-30 months of full production.
If Horizon had been on it's usual schedule, that time would have only been 17-18 months. So a lot of extra dev time.
Now of course they had to deal with covid, so that would've slowed production down a bit. But still. I think the extra dev time shows and hopefully continues to show as more details are revealed.