@Zhaoshuais
Touma totally doesn't always win, that's why I laugh at people who call him a Gary Stu. You only need to take a look at the first volume, who has three fights, to see how most of his fights go in the series:
1) Touma vs Stiyl: Touma initially surprises Stiyl with his IB, but that's immediately countered by Stiyl's Innocentius, which IB can't fully destroy as it regenerates from the runes. So the first battle on the series is also the first time Touma's power is not enough to win, that was quick. Touma wins through smarts.
2) Touma vs Kanzaki: Touma gets stomped, hard. The most he manages is to get a punch in a distracted Kanzaki which doesn't really do much (in the anime he doesn't even manage that). So Touma loses his second fight of the series pretty hard. That didn't take long.
3) Touma vs Index: Touma's IB is stalemated by Index's Dragon's Breath, which is slowly damaging his right hand. He "wins" thanks to Stiyl and Kanzaki's help. So he already needed help from allies to win his third fight.
So yeah, it's not that Touma "seems" to be in danger from weaker opponent; he's in danger from weaker opponents, sometimes even more than from strong magicians, esper. Remember that the people who have defeated Touma include the "powerless" American special forces, which in other LNs of this genre would get slaughtered by the MC to prove how useless they are/how strong the MC is. You continously overestimate/underestimate certain Toaru characters, which leads me to believe you might not be looking at the stats of the two fighters before you make the match and going by how strong you believe them to be. You should always check their stats to avoid making stomp matchs like this on accident.