3) What do all the quotes about improper application of iyun skills have to do with this discussion?
4)Bekius ensures that you know at least everything decently well.
It certainly does not. It may be something you should do, and it may give you certin tools going forward, but a cursory reading of many complicated sugyos would not qualify for ‘decently well’.
5) Contrary to popular belief, bekius does not only have to consist of gemara and rashi. I also learn tosfos bekius as well as many other mefarshim and sefarim.
I don’t only read through popular novels in a few days. I also skim thru textbooks on rocket science in my spare time (with not much of a background in science). I find it very illuminating.
Yes, you can read thru a tosafos or other complicated seforim quickly, and glean the basic idea of whats being discussed. That’s not learning tosafos. For that you read kitzur piskei tosafos.
6)The problem with iyun is that it is much harder to retain the knowledge one acquires due to the difficulty of remembering every diyuk.
But that is hardly the point. Being medayek properly will lead to the proper understanding of the sugya – which you retain much better than randomly memorizing gemoros.