As this is turning into a discussion of seoi nage, here is the secret to seoi nage.
Uke is drawn to tori, tori does not go to uke during kuzushi and tsukuri (which are really not distingishable in a practical sense).
Keep that in mind when performing all forward throws in their "canonical" or fundamental forms. Which is what 99% of us should be doing in the first place, myself included.
I've done seoi nage in most forms for 25+ years as a tokui waza, and I still don't do "Koga" seoi nage. Everyone post video of you seoi nage and let's see how many make the fundamental error that I note above. If so, drill until you burn that out of your system, then you might want to attempt Koga's version. But if you drill the basics that much, you will probably be pretty happy with your seoi nage in randori and shiai.
I used to use Kosoto Gari a lot more than I do now, but I'm making a comeback with it due to teaching it lately. I had forgotten how much I liked the throw. I also do Nidan Kosoto (which is Kosoto Gari anyway). On the common combinations such as Hiza Guruma/Sasae Tsurikomi Ashi to ashi barai, Kosoto Gari works well and is often easier to do.
Agree about the tai sabaki in Seoi Nage. Many,Many forward throws are taught statically or with the forward pivot and result in basically lifting uke then thowing (O Goshi and Seoi Nage are too worst offenders). I teach back turn tai sabaki first, then apply it to O Goshi and Seoi Nage, it works well, and trains tori to draw uke to him instead of going to uke. This works well also because the most basic debana is uke moving forward/pushing.