No, absolutely not. Japanese games were not the reason that the PS3 and X360 sold about the same. And the lack of them on the Xbox One was definitely not the reason the PS4 outsold the XB1 so heavily.
It's one of the big reasons.
In Generation 7, the XBox360 did well because:
-It had better first party support than XB1
-It had almost the same 3rd party games as PS3 (both Japanese and Western)
-It was often priced better than PS3
-In Generation 8, the XB1 did not do nearly as well because:
-It had inferior first party support than XBox360
-The PS4 had more 3rd party exclusives (especially from Japan)
-It was priced worse than PS4 at launch, and about the same shortly after that
The main things that matter are software and price. The PS4 had quite a few games that the XB1 didn't. The two systems are so similar in a lot of other ways, that the games that are exclusives end up being an obvious advantage. A lot of those exclusives were Japanese 3rd party games.