I'd say that if any genuine issues pertaining to band members exist (that's if) then this includes both Heath and Pata.
There seems to be general reluctance on Pata's part to really feature; he shows up, he does his bit, he's by far and large extremely reticent whether with his bandmates or the fans. I didn't follow Ra:In so I have no idea how he's like when he's with them, but where X is concerned he seems very "meh" about it all.
Whilst Heath wasn't there from the start, IMO he's as valid a band member as any of them. He's a skilled musician who has enough longevity and rapport with them to count as their bassist. Bonafide. I'm not saying this to discredit to Taiji - hell no, the guy is an awesome bassist and his tenacity in the scene is to be admired - but I doubt there would be much chance that he would ever replace Heath. Call me cynical but I believe that Heath's whole wanting to leave the band could have simply been a cleverly executed PR exercise to get fans on board. I'm guessing that for whatever reason he had to change management anyway and suddenly it occurred to someone that this could be the springboard for a fantastic PR stunt. And it was, because it worked.
And with the aforementioned worrying phrase from Yoshiki, could this be a case of 'twisting of words', possibly? It's not like the media isn't renowned for doing this XDDD whether deliberate or accidental. And especially as English is not Yoshiki's first language, things easily get lost in translation, misinterpreted and then blown out of proportion.