i’d say microsoft is the biggest threat because they hold a lot of critical data… if oracle snuffs out of existence, companies can probably migrate reasonably easily (don’t get me wrong there would be gnashing of teeth but alternatives exist), CRM there are EU alternatives (ERP, whilst different, is i think a superset of this and yall have SAP which is german) which tend to throw money at companies wanting to switch, adobe… i mean, they don’t really hold business critical data - it’d be disruptive, but not catastrophic if they disappeared
microsoft however hosts huge amounts of business critical data - email, one drive, sharepoint, office, and of course windows: it’s easy to say that email migration is easy, foss alternatives exist for all of this, but the data is particularly problematic and getting users to embrace a whole suite of new systems is pretty difficult