Could ECW have saved the Invasion?

Had they not had ECW and WCW join up to become the jobber faction known as The Alliance and kept the angle as a very distinct WWF vs. WCW vs. ECW and let the ECW guys brawl and act like their characters would it have made up for the watered down WCW part of
the angle? I mean ECW levels of violence on a national stage would have been different compared to WWF and WCW and brought a dangerous element to the angle. RVD was already over as Hell after one match. Maybe the same could have been true for guys like Sabu
(if they signed him), Raven, Taz and others if they left them actually
do what they do best. Could ECW proper have kept the angle alive and intriguing?

No.  If they had the star power to sell tickets, the promotion wouldn't have died in the first place.