Pretty sure they couldn't lose, even if they never figured out the advanced weaponry. After all, they managed the original ambush-and-kill of 750 aliens (assumed, based on "leftover" weapons") with only the tactics and weapons they already had. They repeat that feat, say, six times and the invasion force is toast, even with no new weapons or tactics.
Of course, it isn't quite that easy - the aliens might not be grouped together or positioned right to replicate the first event (and whatever other variables they took advantage of to take out the ship) - but neither will the aliens be supporting each other, and they may not adapt their tactics all that much - coming of age ritual, to me, means ceremony and ritual and not that tolerant of changes. And how often they can replicate the event anyway will depend on how much it actually cost them, in resources, recovery time, and casualties - it will be a lot longer if they have to raise replacements, than if they recruit, for example.
On the other hand, they very well might be able to figure out the advanced weaponry. And they will be working together, communicating successes, and they have examples of some tactics that the new weapons work with, both what the aliens used against them, and what they used against the aliens that they couldn't counter. They can use the information to adapt tactics sensibly - I mean, it's not like they just found the weapons, and are making up tactics without a clue, they've seen them in use.
So even if they only had, what they had when taking down the scout ship, they have a pretty good chance. And as a bonus, they have increased their own firepower by recruiting survivors and making alliances with other tribes, they will gain more again by picking off aliens and recovering their weapons, and they will better their weapon handling and tactics by observing the aliens fighting, and by innovating - which aliens in the middle of rituals (emphasis ritual) will find a lot harder to do than if it were, say, war.