If you look at all the summons throughout the series, you see that there's a core set that appear in almost every game (Ifrit, Shiva, Leviathan, for example) and then some unique ones that only appear in one or two games (FF4 - Azura, FF6 - Valigarmanda, FF7 - Knights of the Round, FF8 - Doomtrain, etc).
So Knights of the Round was never really 'left out' of FF8. FF8 included the usual core ones, and a few uniques, just like FF7 did, and so did the earlier FF games.
Knights of round
Knights of the Round summon from FFVII as it does the most damage any summon will ever do if it's maxed out doing 13x 9999 damage.
Either but i would say Knights of a round, for damage reasons even though it takes forever to charge.
Yes.
Yes, nothing else will do. You cannot reach the island in which it is kept any other way. However you can defeat Emerald Weapon and trade the Earth Harp you receive to a man in Kalm, and he will give you three Master Materia, the summon one will allow you to cast Knights of the Round, though you won't have a separate Knights of the Round materia.
1 hit from knights of the round will do it
Definetely.
Yes.
Yes.
Very weak.
Yes.
Yes.