Ya, a better concept would be a "contribution" output that's shown after an event ends which showcases heals and dmg done by the party members. If a party member falls under the treshold to be worthy of the reward they obtain nothing. So say in CM or the final dungeon for story a person stays at the start an accumulates no dmg or healing throughout the encounter. Because of this they would obtain no tome rewards because they did nothing to contribute to the party.

Of course people have to go afk at times so for that there could be 2 stages,
50% reward and 100% rewards.

In terms of CM and the last dungeon the 50% reward could be obtained by at least helping with half the dungeon so while yes leechers may still exist to an extent, if said leechers want the full reward then they might as well help the whole way.

100% will be for those who help throughout the whole dungeon and pull their weight but done in such a way where the overall battle output would allow for each player to gain 200% of the 100% they need so as long as they help the whole way there is no issue.

But then they could also add caps to each stage so a person can't accumulate 100% through some exploit such as 25% at the first part, 50% midway, 75% near the end and the rest gained through the final boss fight.

This would encourage people to actually play, the MVP system does nothing more than add another troll concept because said trolls can be like, nah I'm not voting for anyone but beg everyone to vote for them, of course they won't and then snarky remarks and negative communication will occur and it just in the end doesn't help the situation.