"For those interested in an 'old school' approach, the DM may require wizards to memorize specific spells for specific slots."
Solves both "problems," in my opinion.
I wouldn't say it solves the problem, because this is not applicable on a player's
individual basis. If player A uses this option, she's simply hampering herself compared to player B, and that sounds like a "punishment" for only wanting to play a Wizard like it has been in D&D for more than 30 years.
But even if accepting to use this option on a group's basis (all casters or none), if we assume the current casters are balanced with non-casters, it will be a serious downgrade. In fact, the 5e "upgrade" was paid by quite a lot less spells/day compared to previous editions. That means, to use this "traditional Vancian" option, we need to compensate the casters.
Last year I suggested in this thread
http://www.enworld.org/forum/showthread.php?340467-True-Vancian-spellcasters to grant 1 additional spell slot per spell level to someone choosing to cast in the more restrictive "traditional Vancian" way. The general opinion in the thread was that this was too much, but I still have the feeling that it might even be too little.
Back to the topic at hand, I find that you tend to use all of your slots for the same type of thing, but you have fewer wasted spell slots over all, so it's pretty much a wash when it comes to total versatility.
Agreed.
It's all part of a slow trend in gaming to want decreased randomness, or less chance of mistakes. In previous editions, you had to accept that sometimes you didn't have the right spell at the right time, and the underlying idea was that the main method to improve your chances was
player's effort, i.e. spending more time investigating what might await you and carefully plan how to maximize your chances.
The current trend in gaming is that people quite dislike randomness in general, and more specifically hate the idea that they might sometimes make a planning mistake. Other symptoms include: common preference shifted from random score generation to point-buy, layers or rules to save the PC from chance of death, intolerance towards characters abilities that work only on some type of monsters, and "all characters must be equally good in all pillars" mentality. Many players nowadays are very scared that their choices are wrong, but instead of thinking they can adapt their characters to the world, they want the world to adapt to their characters (i.e. blame the DM because she didn't change the campaign to suit your PC super-specialized in killing infernal robotic half-undead/half-golem flumphs). They want to play the game with a feeling that no choice is wrong.
Which is not a bad thing per se, but if you do enjoy a challenging game, finding yourself in a game where no choice is wrong actually makes it minimally challenging.