I think the best way to break this whole thing down is to say that there is nothing wrong with training your horse yourself/ wanting to be very involved, sending them off to a trainer and not seeing them at all until they come back, and all the grey areas between. Everyone may have their own opinions and preferences, which you are entitled to, but in the end they are still preferences and opinions.
What it comes down to is the individual horse and person. Some people are not equipped to train a horse at all, maybe because of age, physical conditions, lack of knowledge, plain disinterest, etc. Some might be willing to learn with their horses, some might just want a nice horse to ride out on and have no interest whatsoever in learning how to deal with a problem. Trainers are here for a reason, to train horses. Some want to train riders, too, some just want to deal with the horses. But there is nothing wrong with utilizing a trainer's abilities, whether it's because you are solely interested in the product of the training or because you're interested in the process.
Personally, I have seen plenty of people form strong bonds with horses that they bought already trained. There's much, much more to bonding than just teaching them to do something like accept a bit and do a leg yield, although it definitely can help for some horses and some riders. My best friend bought a teenaged arabian gelding from a trail riding business because she fell in love with him- she had nothing to do with his training, but they have an incredible bond. He was a bit mangy and indifferent when she first got him, but after being in her care for a while, he literally blossomed into a sassy, joyful little horse who loves his job and his human. I'm positive it's because he was allowed to bond with one person. She also has a young mare who her family bred and raised and who she trained/ has ridden all the mare's life, and they also have a bond. I have seen trainers who did not bond with their horses at all, keeping their relationship 110% business. No bond, no love, just respect, and that was all they needed.
I am of the personal opinion that if you can be involved in the training of your horse, even if it's just checking on them once a week/ calling the trainer for a quick report, do it. My arabian is 6 years old, I have had him for 4 years, and is only just getting kicked into gear, because I refused to settle for anything less than a trainer who would teach me to teach him. I'm very interested in the process and even in becoming a trainer some day, so I was pretty firm on that. A lot of people would have just sent him off to a trainer for a month or two and gotten it over with, and I don't think that would have been the wrong thing to do, I just didn't want to.
I can understand if someone was showing at a high level and just wanted to get a trained horse to work with, just like I can understand how someone might want to have a sane, trained trail horse so that they could enjoy their riding. It's all preference and opinion.
I understand what you're trying to say, OP, or at least now I really do- as it has been pointed out, your beginning to this thread was kind of fuzzy. I am not saying that you are wrong, either, and I don't think anyone else here is trying to beat you down, despite the defensive responses... And of course, everything I've said in my little essay here is totally my opinion and I don't expect anyone else to share it. This is a good thread, though. I'm glad you made it.
And so, my little book ends. Lol. Sorry for that.