I've always seen efficiency in terms of the main game as focusing on what works well in getting through the bosses / routes with little effort. For a personal example, way back in 2016 I used the old version of the Black / White tier list as kinda a gut check, not knowing any pokemon in Unova, so the list served a check to see if something was worth spending my time with. Now, the tier lists have really moved beyond that first version and are far, far more helpful (especially the revised version), but I don't really think anything involving the daycare is really efficient in any in-game sense. I'll be honest, if you tell me that breeding a Pokémon is the best way to use it, I'm probably not using it. If I have to spend time breeding and leveling it up as opposed to something I can catch/get and throw into a battle, I'm going to go with the faster option. I can catch a good pokemon and go into battles confidently rather than spending time with something else.Yep, casual players aren't speed runners and likely don't give two shits about maximizing efficiency. That's for novice players who want to do well but also enjoy the game, the players whom we actually should be helping and keeping in mind, not speed runners or casuals, at least that's my opinion. Like why even make a tier list if it's not to inform people so they can make better choices in their gameplay? And who are we informing if not people who actually want or need it, such as people who want to actually know how to get through the game more easily?
Some of the mechanics in Pokémon are not really important to know when plowing through the story mode, On average, I usually take 15-30 Hours to complete a story mode in a Pokémon game, and I've been playing since 2002. Nowadays, I don't want to waste time on something that takes actual time to grind. The daycare is an afterthought for my story playthroughs, If something takes explicit time to grind up I'm not doing it. I don't care if the Pokémon is better, ill just use something else. That's how I look at these lists, if something takes too much time and effort to use rather than clicking A on the enemy, it is less efficient. I look to these lists (even in testing forms like this) to see if something is taking too much time to go through. For example, Slowpoke is something that in GSC appears to be something better to get later on in the game, I want to know that, it saves me time grinding a slowpoke through the early game. Time is a major factor here in terms of efficiency. If I'm spending time grinding or breeding a Pokémon, that is time I can be doing literally anything else.
My answer here (and goes for what I said before) is that efficiency is broader than just what is the "best" way to use a pokemon. Being given a pokemon is honestly the most efficient way to use it. There is 0 effort on the player to get and use it. Anything more than that is spending time on something when I could be using a Pinsir or Snubbull.1) You get to use an Eeveelution much earlier, if you're going the Espeon or Umbreon route. We have already broached the topic of earlier or later access to a Pokemon, and I think considering earlier access to a powerful Eeveelution shouldn't be easily discarded. Between the higher base happiness and the ability to control the place where they're born so you can just level up in that particular spot to double the happiness gains, you can get Espeon or Umbreon earlier and at a much lower level than you likely would in the main playthrough. I can test this out for you if I'm not convinced.