Austin, I should add that decades previously (in the 70s) I had done O-level music (the then public exams done by 16 year olds in the UK) which as Aquarelle commented very recently had lots of theory and harmony in it back then, so my self-taught Grade 6 involved largely "revision" from long ago... I think the present G6 standard is pretty similar to that of the old O-level (I still have the O-level papers!).
Yes, there is indeed a large jump from G5 to G6 in that G6 involves harmonisation, figured bass etc. whereas G5 is now just "rudiments" based, but I was aware of this before starting out.
The question about the gap between G6 and G7 is an interesting one. We've discussed this before on this forum and forumite Sbhoa said she found G7 easier than G6. The extra harmonic knowledge required is indeed very small. The very useful site https://www.mymusictheory.com/ (my second main source of help after the Workbooks) also says somewhere the difference is small. In fact, I find some of the G7 harmony questions harder than G6 even though no more formal knowledge is needed. This is because more stylistic awareness is required and it's more open ended, for example in adding passing notes convincingly to a cut-down Bach chorale, or adding a melody above a given piano accompaniment. It'll be interesting to see what you think.
I'm also planning to do Trinity Theory Grade 8 - the Trinity syllabus is rather different from ABRSM with more questions on form and less on harmony.
You have much more ambitious goals than I do! All the best with them all (oh and many congratulations by the way on your Grade 8 Piano result which I saw on another thread). Grade 8 Piano is another ambition of mine, having done G7 Piano some years ago too, but it will have to wait until I retire, which sadly is no time soon. Let alone the violin, cello and guitar which I never find time to practise at the moment...