PS5 hasn't even launched so that would be a pretty random guess at this point. But I wouldn't be surprised if PS5 sold less than PS4.
more competition and a higher price, obviously not the be all end all but I really dont think ps5 will sell more than the ps4
The thing about more competition (from Xbox) seems to generally be based on Series S/X launching/doing better than XBO.
When it comes to being appealing to a new consumer, that makes sense. But to win back an old one that switched to Playstation this gen, that's probably more complicated. Now if you have to chose, it probably comes down to which library you prefer.
Gamepass is also an interesting factor. It's available on Xbox and not PS5. But it's also on PC.