I see your point but HE(palpatine) didn't think it was risky because the second death star was fully operational, AND he didn't realize that a bunch of primitive ewoks could take on storm troops with rocks and slingshots.....
honestly if you were the emperor and you had a bunch of troops on endor would you expect that the ewoks would be able to take on storm troopers.
Luke obviously became a quasi Jedi at the end of ROTJ, but so was Galen. Both men had not realized their full potential. Marek's life was cut short when he sacrificed himself to begin the rebellion. But, I believe he was strong enough to begin Luke on his journey to become a Jedi Knight. Obi-Wan was dead at the time he [Luke] arrived at Yavin IV and if Galen was there, he be the closest person to a Jedi other than Yoda. I believe that he would teach Luke certain powers of the Force and lightsaber techniques that he knew. Yoda would have had a more refined student than the one that he met initially. The Luke that Vader met on Cloud City and finally on the DS would have been far far more powerful, than the Luke in the ESB & ROTJ. If Force Repulse is a power that Galen knew well, it would have been one of Luke's more devasting abilities.
Other than Dooku and Obi-Wan, Galen was the only other Force user who was able to defeat Anakin/Vader in Force and Lightsaber.