I can see what you're saying, but Mash in my group dies pretty fast and does crappy damage. She's capped at 40 and has been for a while now. I keep her around a a backup in my group, but she just can't handle stuff like other characters can. If she's supposed to tank, then she doesn't do it very well at least in the content I'm in now. Ultimately, it doesn't matter. I did enjoy building her up and I'll continue to do so.
My problem really with the game is that with what we're allowed to do, the drop rates are terrible and with the number of units that can/should be leveled up it's so hard to actually do so. Now, I understand that not all servants should be leveled to the absolute max, but it's hard to even get one to that level, let alone two. If you want to keep playing, eventually you'll hit a wall even if you're only playing a short amount of time per day. I personally place one session a day and generally until I run out of AP (even if I level up, I stop playing and hold that energy until the next time I play), but I don't feel like I can make much progress in what time I devote to the game. It just doesn't let you do that. The grind is serious and severe with drop rates that are atrocious. I tried to grind out some gold stones to level up Emiya when the Archer dailies were up and I didn't get 1 of them. Not 1. I dread to think of what it'll be like once I get Artoria Alter or Zhuge to their next level. When hitting that wall, what else is there to do? Level another servant until you hit that wall again with that character? Just seems like crappy design all around. I don't feel like I'm making progress and what little progress I am making hasn't made doing anything in the game much easier. I was hoping to at least get another servant to work on since I'll be at that dead end again very soon, but getting new units is hard and even the rate ups don't seem to mean anything if even getting a servant is difficult in the first place.
At least with other games, I felt like the little time I spent in it was fulfilling in some way. This game almost encourages the player not to even bother.