Yeah, I kinda see this little spat from both sides, you really shouldn't be able to get easy wins by sniping future opponents before they get to fight, but this was also due to an inadequate barrier and the first 7th year being a dipshit letting her unleash her full power, and if that is enough for a TPK, well, the 7th years wouldn't have won in the first place, but letting him sub in 4 more students seems like the best course of action here even though neither side would particularly like it (to the 1st years kinda feels like he gets to choose who fights after seeing the current results unlike them, and for the 7th years they lost 4/5 of their first picks instantly).
I actually enjoyed this little spat, felt more well rounded than a lot of similar ones I've seen, not to mention that as much as this pulls out the 'Oh noes they were actually OP!' gag, the 7th year underestimating a first year, even if in an elite class, does make sense, and at least the eventual harem is also being built to be a serious threat rather than useless without MC until the plot needs them to be strong.