A good teacher can make a big difference to how a child experiences a year of their life but the long run effects on them are unlikely to be large. Children of normal intelligence learn to read easily once they’re ready, just as you can cover grade school math in under 40 hours with a normal twelve year old.
A reading child can begin to write and type earlier. They can be exposed to complex computer use instead of simplified apps. They can use more advanced materials to learn other skills earlier. They can gain a ton of knowledge from the extra years of reading. And even if they cannot understand much at 4 (which of course depends on the kid), they can at 7 or 8 - being fluent readers by then gives them the advantage of consuming many extra books and richer ones.
There are also psychological components. Until school starts the parents have significant influence over 'cool' skills, important values, 'fun' things to do, etc. Schools rarely breed love of learning and peers often push away from it. Learning at 7 creates risks of it being perceived as less cool or being consumed by other activities and not catching. The time before school is hugely valuable imo. And reading earlier gives the parent another tool to teach by providing books.
It is true that the earlier you start the more time teaching takes. But this time isn't only teaching reading. It is excellent bonding time if you don't turn it into an authoritarian war zone. It teaches focus, overcoming obstacles, etc. On the whole, I think it at least holds its own with other activities parents spend time on with their toddlers. The bulk of the challenge is getting the kid on board. Buy-in and motivation matter far more than any specific method since without them the risk of the effort hurting the relationship or their love of learning is too high.
I used a method of my own making. It probably wasn't the most efficient, but it was always tuned to the kid. My oldest was fully decoding in late twos and reads a ton now in late sevens. He naturally memorized words and we added phonetics later. My youngest is decoding short words with basic sounds in the early threes. He is not a fan of memorizing, but took to phonics naturally.
Singled me out because I liked math and she was an English and Spanish teacher.
I had never gotten a C before, but that teacher in a panic admitted that "I wasn't good at her class like I am at math". In reality she was targeting me for some reason and giving me minimal participation credit despite participation.
By the end of the class, enough students complained she stopped teaching Spanish 1. And she still teaches to this day 11years later.
If you give teachers no autonomy, you will turn teachers who want to wait or push based on situation to the ones who don't. Or they will simply leave.
Just like with any other job, you either command details or you have people doing own decisions. Cant have both.
All of the calls to alternate education methods fail to recognize the weakest link in the education system: teachers. Teaching methods are not designed just for kids but also for teachers.
Almost any method will work wonders with good teachers who know when to wait, when to push, who are competent and empathetic. Methods need to be tested and proved to work with below-average teachers to be considered a solution.