Yup. bad luck - trade away.The biggest issue I see with only selecting 2 rucks, is if there is a team who currently has 2 very good rucks, as well as a good R/F. That would be unfair on them being forced to drop one. But again, it encourages trading and they can use it to strengthen another area of their team. Everyone is in the same boat here...
10 teams has worked perfectly fine in a 6/8/2/6 set up that I've seen across multiple boards. As I said earlier, I think the initial crap auto-drafting made things a little lob-sided, and now people are coming in with very weak ruck departments.
To be honest, we could just leave it all and say bad luck to those particular players, and either trade or go to the draft in search of rucks.