Sony is the market leader and MS a distant 3rd, Sony isn't worried about them.
They don't give a fuck about MS E3 presentation, the new game exclusives they announced were only another Forza Horizon (which looks great) and a bunch of CGs, and a bunch of multis or timed exclusives that will end on PlayStation. Nothing that will require them to tweak their plans.
Sure, Game Pass will get nice games for this an next year. But Sony's gaming division makes way more money than MS gaming division and Sony gets more money from their game subscriptions than MS and does it in a more profitable way, signing mostly older games.
So no need to worry or to rush, they will have their next game showcase when ready or when they consider it. As of now Sony doesn't need to rise the hype because they are selling out in a few minutes all the consoles they can produce, so maybe are saving the big announcements for once they have offer and demand more balanced after solving the chips issue.
On top of that, big companies plan ahead their main stuff several years ahead (to decide if they or when they will release a console revision or PSVR2, or to set up their exclusives roadmap, or to decide the next gen PS Now changes and focus) and only do small tweaks like making reveals a bit sooner or later, or delay something, depending on short term circumstances.
In fact, Sony skipping E3 did help MS to giving them more attention and 'win E3', which means nothing.
If Sony would have considered it was important for them, they could have been there to reveal the first gameplay of Horizon and GoW, announce there Death Stranding Directors Cut and the Firewalk game (that can be released next year, they have been working on it since 2018 so the game announcement must be close) plus to show more of some big known 2022 exclusives like GT7 or FFXVI and maybe announce Insomniac's 2022 game (Spider-Man 2?) and TLOU2 Factions, plus the reveal of the next CoD. Without big surprises or changes compared to what we know or can assume, they would have 'won E3' again.
But they didn't do it because didn't need it. They'll do their own stuff when they consider it's the proper time to do it, and away from other companies presentations to make sure they get the full attention.
And well, they didn't cheat because there aren't rules related to when a company decides to show their games.