Some time back I downloaded a mobile game called Yu-Gi-Oh! Duel Links. Duel Links is essentially the Yu-Gi-Oh card game using its relatively recent speed format. At the time, I was very dubious about this type of game existing as, having been a fan of the card game in real life, I couldn't see any way Konami would do it well without choking the player with paywalls or restricting the experience. Once I opened the game, I was met with a mostly standard fare experience. Indeed, it was the card game as I knew it, but it was severely hobbled by the selection of cards available, with ultra rare cards including choices that were strong back in the early 2000s. What was more, the NPCs were laughably easy and the speed of duels overall was yawn-worthy. Needless to say, I wasn't impressed. It was just another free-to-play.
Fast forward to late 2017 where the game is given a surprise PC release. The original experience had been so forgettable that I didn't much mind downloading the game again for the novelty of seeing what had changed, so I did. What I was met with was a pretty similar experience, one that wasn't flawed in the first place. The number of cards and archetypes available had greatly expanded, several new characters were available, multiple events were taking place at once, it was a hell of a time to get back into things. To this day, Duel Links is my most played game on Steam by a long shot, and also represents what a free-to-play should be.
There have been a lot of free-to-play titles that have interested and even surprised me over the years, but in most cases they all fell victim to the same problems. The first of these problems is probably the biggest, and that is that difficulty is an illusion. Rarity is such an important aspect of free-to-plays because they largely dictate how easy it is to overcome obstacles. Most games will throw a tutorial your way, immediately followed by the game throwing a UR or SSR your way that steamrolls content far more easily than the normal and rare units that you are given off the bat ever could. While this might seem like less of a problem and more "just business", content being trivialized also leads to the gameplay itself being trivialized.
Sword Art Online: Memory Defrag is a wonderful example of how this illusion of difficulty is a detriment to the game itself. Memory Defrag is an action RPG, one that allows you to attack, block, dash, and parry. This is interesting as it essentially allows skilled players to go into battles with any unit and take no damage at all, even if only just for the fun of the challenge. This is great on paper, as it allows the player to use whatever units they want and clear content as long as they are skilled enough. However, there is a caveat. Memory Defrag is still a free-to-play title, and in the same vein as most of its brethren, it also has automatic movement, automatic attacking, and units of higher rarity that blow lower rarity units out of the water regardless of how upgraded they are. As such, the player is discouraged and even punished for trying to play the way they want to. The one that games most efficiently reaps the most benefits as they can meet time limit and damage bonuses more easily, potentially without even playing the game themselves. This might not seem like much, but meeting these goals grants hefty rewards; as such, any sort of difficulty can only really be created by the player, and in these cases they will not be rewarded for it.
Duel Links, on the other hand, subverts this illusion. The game itself does very little to actually differentiate from this. It has automatic duels with its NPCs, normal cards are only rarely viable, and not playing meta decks (the top performing decks at a given time) puts you at a disadvantage. What makes it work here, though, is that, regardless of all of this, the difficulty is in tact. This is true for a number of reasons, from cards not having been viable in the past proving to be very useful and easy to obtain going forward, the emphasis on PvP, and the fact that automatic duels don't actually affect the core game itself. All of this say, the game itself cannot be trivialized because the core experience requires player interaction. If the player doesn't play actively, they won't get anywhere.
Mobile game companies generally have no interest in making a game that the player will find fun- at least, not in the case of the free-to-play industry. Rather, they would prefer to make games that occupy the player's time with a gameplay loop whose only variance lies in the RNG of gachapon-style pulls, as that is far more profitable. To call it a "gameplay" loop at all is a bit of a stretch as gameplay implies even an iota of choice. Though, if you consider using your credit card as a choice then mobile games have some of the most engaging and complicated gameplay loops out there.
Probably the most blatant example of a company making a mobile title to simply fill its audience's time is the infamous Final Fantasy: All The Bravest. If there was ever a game that had no interest in veiling its identity as a cash grab, ATB is it. The game involves rubbing the screen to essentially throw your units at the enemy. That's it. The player simply rubs the screen, kills the enemies, rinse, repeat, until their team either dies or they complete the level. Should their team die, they can either wait in real-time for them to come back or buy an item (with real money) that does so instantly. This is disregarding also being able to buy adventures and characters for this "game" that almost literally just consists of bright lights and micro-transactions, and of course that there is no customization to speak of, party or otherwise.
Of course, this isn't to say that Duel Links is the only game out there that handles its free-to-play status with stride. Idol games like Love Live, Bang Dream, and iDOLM@STER, apart from being rhythm games, appeal to their fandoms on the basis of pulling their favorite characters and interacting with/using them. Fire Emblem Heroes, while not having quite the depth that the main series has, sparks uncontrollable conversation among its fans about strategies and characters even still. Kantai Collection, Hearthstone, Granblue Fantasy, among others, while all of these games do indeed have their problems, they are far more functional games than the swarm of other free-to-plays that have no interest in actually making a fun gameplay experience. There is a reason why mobile and non-mobile gamers are often segregated from each other, and hopefully one day that will not be the case.