Yes his doctines are the same.
However, he must be taken in the context of the whole where he might seem to discent from lets say James he really isn't and the person who thinks he is is viewing his writings wrong.
But Marcion like to only quote Paul because he could take Paul out of the context of the whole and have Paul "support" his own personal view.
The only groups that would claim that are Muslims (who accept Jesus as "Messiah" and prophet, but believe that people corrupted the scriptures, and Paul derailed "the true Gospel" with his "philosophy"), and the Ebionites, which were an ancient sect that believed in a Judastic Christianity (similar to today's sabbathkeepers), but eventually realized they had to get rid of Paul in order to really make it work (rather than reinterpreting him).
This has essentially been resurrected today, with a site called judaismvschristianity. Is that what you're asking about? (I don't think anybody who argued something like that would be allowed to post here for long, though I haven't been here for awhile to see who's been posting what).
Think some catholics that have been posting here seem to imply that the Non Catholic churches have made Paul the sole speaker of authetic Christianity, that somehow he and we neglected to include james and other voices in the discussion!
Although this wouldn't pertain to most of the NT since little (if any) of it was written at the time, I can only think that the same principle would apply in this case as it would have when Luke commented about the Bereans in Acts 17:11.
They were more noble because they didn't merely take the Apostle Paul's word for it, but rather took the time themselves to search what scriptures they DID have (namely the OT) to see if Paul was "on board" with them.