Many of those are really broad comparisons.
I could say Scooby Doo travels from place to place, encountering problems only they have the skill set to solve and has companions that sometimes get into trouble. Hell in one series he even travels with a more inept, useless version of himself. But I wouldn't say Decade was intended to be the Scooby Doo of Kamen Rider.

On the subject of Blade, couldn't he just borrow the Spirit card off of Hajime???

No. The Battle Fight compels the participants to fight. He doesn't want to risk it.
Also, the Spirit Card only has one human form. He wouldn't transform into Kenzaki, he'd transform into the same person Hajime is.