Well, considering that five tokens is no longer
absolute minimum pay for surviving a mission (even completely botched)... yeah. Also, I would not say that it's anywhere "usual" amount being 10; let's take the last batch, for one. M17 paid 6 tokens for the mission; anything over that was just the spoils of war - and M17 was to be considered one of the least botched missions, practically perfectly accomplished. M16? Again, ~6 tokens per person - which was probably to be 5 were it not for a death. M18? Well, this one varied wildly in pay; some people did not get paid at all, some only very little, and the top participants were paid
whooping 9 tokens. And see those "three dead men", whose "...pay would be 9 tokens combined"? That gives the perspective of what is the current baseline for "average" performance.
Thus, these days it would take 10 (give or take a couple) average missions or 5 exceptionally good ones (see the above on Feyri's and Morul's payment in M18) to reach 50 tokens - without spending any of that on any additional equipment, which would severely limit the character's usefulness. Now, I must admit that supposedly black-ops have a higher rate of pay on average, and by their perfect scoreboard so far one could claim that it is even easier to earn tokens there, but then it'd take a character dedicated to black-op missions to earn tokens that fast without straining the limits of possible, and they'd might have little incentive to buy the Avatar in the end.
Also, I would like to note that the statistics provided by Aoshima are all prior to Assault on Hephaestus and formation of ARM. The pay simply ain't no good these days!
((And that one was a year-long mission, if I got it correctly, and it was a "double-long" one. The pay should be "halved" and considered for two separate missions; even the level-up came twice for it, IIRC.))
So, all in all, while I agree that making them cost 50 tokens would make them even more exceptional, I would still argue that it would simply put them outright out of the realm of realistically possible. Plus it would leave too large a gap between "equipment tiers".
So, my regular mantra: please don't fix what isn't broken!
((I might find it bearable if it turned out something like 35 tokens. But at that point it might as well be negligible of a difference to necessitate all the problems with that change.))