Actually, I disagree with the OP. Risk management and position sizing (RM&PS) is never of no use. Even the worst trading strategy in the world would be less bad with RM&PS. 
I doubt any amount of RM&PS would make these very profitable.
Is position management part of risk management?
Successful trading requires you to cut your losses / keep your losses small(risk management) and riding your winners (not taking profits too soon). There's no way around this. At the end of the day/week/month/year you tally up your wins and losses.
Simply put, a successful trading system/approach/strategy then needs to either have:
a. A high win rate if your win/loss ratio is equal. A
very high win rate if you risk/bet more than you seek to gain. Typically associated with scalping.
b. A low winrate if your win/loss ratio is say 3:1. This does however assume that you take your losses and keep them small while riding your winners.
Because of human nature, we tend to do the opposite, i.e, let our losses run hoping they'll come around and cut our profits short (getting out too soon). So, low win rate and a win/loss ratio of 1:3 instead of the other way around.
I think it's perfectly possible that many traders could have profitable systems in their hand, but fail to execute them for the reasons mentioned above. And the larger you trade the more these issues compound.
Probably not
the obvious, and maybe very obvious for most. Just pointing it out anyway.
