Francois is not quite grindable,
I also got Matahari in the past event, and even though I did not try to get Francois in this one, I aimed for Terese instead, and I spend 15 hours a day on this game during this event, which is just a little bit less than 19 hours a day on the past event.
And it is actually easier to use all your training points on this one, since you don't need to do 5 min intervals but 30min intervals instead.
So the last 7 days, I had just about 28 hours less than the past event.
My current number of charms is 12k.
A lot lower than the 30~35k required for Terese, and no matter how you see it, there's no way I can get Francois without using any Pots.
I know you get more charms along the way, but with all of the 3 common bosses(which you encounter a lot without paying for any special unit) gives me an average of 4k, by beating lv1~95(Hugue is at 102 right now for me)
And they are getting harder, even with ally assistance, you are likely to have to spend at least 1 extra turn to beat them, that's 50 training pts extra, and most of my allies got 6* units, so they are all pretty strong.
BTW, my Matahari is at lv112, so unless you got other maxed 6*, I would imagine you having harder time than I do.
And I am planning to grind for the Mandogora event that is similar to this one(that 6* is worth fighting for, speed A with poison), so I am already saving up ahead of time, and using various events for simulation to ensure my success in that one.
By simple calculation, 1+2+3+4+5+...+94+95=4560, we know that on average, the random number generator does not even give you charms that is equal to the lv of the bosses, unless you are fighting special ones like Constance and Isabelle.
BTW, I just met my 2nd Isabelle when typing this, and Constance is only at lv11.
Granted, undeadly did not have a really good attitude over there, and Francois really isn't that practical, and no way worth 1500TE, but saying if you had spent time in it you can get it, than no, as someone who played almost all events and had been calculating if one can simply grind to get the 6* units, all past similar events that requires boss fighting are impossible to grind, unless you pay for a special unit first, which gives you more chance of getting special bosses.
I can tell you why boss events are not grindable, it is simply that pots recover 30 mins for you, but TE recover 5mins for you in quest events, so their actual worth in event, in exchange to time wise, is 2:12, that means if you spend 2 pots, you save an hour in the game, but you need to spend roughly 12 TE to get the same result, and obviously, the company cannot ask people who pay to spend ridiculous amount of TE just because they want to stop people from grinding and getting 6*s for free.
Say, if the company is targeting people to pay around $120 to get a 6* in event, that's about 120TE, right? but that only adds to 10 hours, in 7.5 days of game play, and grinding for 18 hours a day, you can shorten that to 16.7 hours a day.
But if you pay $120 for pots in this event, it saves you 60 hours of game play.
So, think of grinding 16.7 hours a day, and on top of that, you need another 60 hours, or 8 more hours a day for the 6*.
Which, will give you 24.7 hours a day.
BTW, the company is not that naive, and generous, they are not just looking for $120, think of the 0.2% chance of getting a 6* in NORMAL card packs, you can tell that they are looking for more like $3/0.002=$1500 for each 6*.
well, they do need to give you some hope in getting a 6* in the events, lets make it $1200.
So, in a TE event, 1200TE gives you 100 hours of time, so you only need to play the game for about 5 hours a day, which is completely normal for a regular intense player that got work to do.
(My job nature grants me the opportunity to use my phone, not all jobs can.)
But for a POT event, 1200TE is 600hours, which in itself is more than the 24X8=192 hours-maintenance down time.
Even if you think the company is just looking for say, $300, that's 300TE or 300Pots, 300Pots is still 150 hours, and is way too easy to get(don't need to remind you of the personal ones, right?) You'll see paid players, those within the 500 ranks, all got 6* in the first 2~3 days.
Anyway, just think of Pots events are 6 times harder to grind than TE events, just because of the nature of it recovering 6 times the time required, if you have grinded for Matahari, you'll know 6 times of that is impossible.
So logically, you CANNOT grind for free to get the 6*s in any events that requires potions, or the company is in real trouble in earning money and will probably fire whoever designed those events.