Beginning

If I was to learn from somebody competent rather than learning to paraglide first, would this have any foreseeable detrimental effect? Essentially, is being mentored a good way to enter the sport?

Not ideal, but yes being mentored is one way to enter the sport. Detrimental effects - Higher risk of injury, Mentor not insured to teach so if you have accident you have no insurance cover/protection and slower progress than if you have PG or Skydive experience. One other issue is where you will/would be flying, some countries require that you have PG license before you can go speed-flying (eg: Switzerland) others require that you have PG insurance which you cant get without a valid PG license.