you are right. If Qatar had not been the host country, it would have been almost impossible for Qatar to qualify for the next round from this group. But they will play at home. At the same time, as host countries, they may be able to exert some influence over FIFA and the referees. And so it is not impossible for them to qualify for the next round. Also, the Qatari team is not too weak. They can play well.
There has always been home or advantage on every country hosting a cup finals just because they want them to go far abit in the tournament but they may not actually win the final stage because by them things could have been gone tougher than expected, i so much believe that that's just the only way to encourage and compensate the hosts as it may not sound well getting knocked out at the early stage, it's a on rare case seing the host country getting to final or winning the cup.