> Apart from personal opinions, is there any evidence this is due to Google sabotaging uBlock rather than a legitimate technical concern (V2 vs V3 manifest)?

Google is an ads company. uBlock Origin is making them lose money...

> Could uBlock implement V3 without losing its functionality?

No, that's why everyone is angry and a ton of people switching to Firefox, to keep using uBlock Origin as it is, since Firefox still respects the V2.