Listen, kick-ass; I can understand why you would think that Vlad should be more powerful than Danny because he had more experience with his power; however, there are several reasons why he is not as powerful as you might expect
Danny was not only inside the portal but also inside a very large working one. Vlad was hit with a small, contaminated proto-portal.
* The only thing Vlad has over Danny is experience; by the end of the series, Danny can go toe-to-toe with Vlad. Regardless of the messed up timeline, he's still in high school, and he's grown much faster.
* Vlad had his powers for 20 years, yet he never gained things like cryokinesis or the ghostly wail. We never even see him with a ghost sense.
* After only 10 years, Dan became one of the most powerful ghosts. The most powerful we see is the barring clockwork. He can change his form, disguise himself to look human despite not being one anymore, create ghost portals with his hands, use a time medallion alone to travel through time, and somehow permanently injure multiple ghosts.
* All of that is after Dan absorbed Vlad's ghost half, so his ectosignature is likely corrupted like Vlad's, making him likely weaker than he would be otherwise (without realizing it).
* Our Danny defeats Dan and gains the ghostly wail 10 years early. Dan mentions at the beginning that it's a new power.
Danny has so many powers because the entire ghost zone zapped him, so he’s absorbed many powers. He doesn’t have them all initially because he’s still growing and learning. Give him a few years; fighting ghosts won’t be a struggle anymore.
Or even that frequent. He’d gain a reputation over time, and I doubt any ghost would want to mess with him or anything under his protection. He might get a few who wish to challenge him here and there, but yeah.
Not to mention how powerful some of his enemies are.
He’d be able to wipe the floor with Vlad pretty shortly.
But lookit his face.