Although it's decent, Leuchtturm is not the best quality paper that's out on the market.
[he says that while avoiding eye contact with angry mobs holding pitchforks]
I've had mixed results with bleeding and feathering on this paper, but then I also insist on writing with a wet juicy nib.
Rhodia, Clairefontaine and Tomoe River are primo quality and hold up very well to any bleeding, you can be assured.
It's very plausible that dilution of ink will help with bleed through.
Ink after-all is nothing more than a solution of water, dyes, boicides for preventing fungi and bacteria to find a nice home in your ink bottle, and surfactants which cause the ink to flow better by breaking down surface tension of the fluid.
Once you add water to your ink, you're reducing the concentration of all of the solutes in your ink. The concentration of surfactants will become lower and therefore the wetting and coating quality of the ink will become reduced. This will make the ink drier and less prone to bleeding and feathering (or spreading) on the paper.
The other problem you mentioned, ink-transfer (I like your description of it), is commonly known as smudging.
If your ink is still wet on the paper and hasn't had a chance to dry, and you brush your hand accross it, this is called smearing. Once the ink dries, and if it doesn't completely set (and cure?) into paper 'A' and can still be lifted off by an object coming into contact (paper 'B'), it's called smudging.
I'm not very well versed on what causes an ink to smudge, but it does have a direct correlation with the amount of dye-load deposited to the paper. If the ink has been sitting and aging in your pen and dehydrating, it will likely deposit a lot of dye in a concentrated fashion, onto the paper, thus causing not only smudging but also bleedthrough (because the surfactants have had a chance to increase in concentration).
Some ink manufacturers in my experience, have a pretty good handle on smudging even when heaps of ink is deposited onto the paper, sailor and iroshizuku are good names in this area. I haven't had good luck with smudging when it comes to Noodlers; Apache Sunset, Army Green, and X-Feather all smudge for me and I have to employ your solution of diluting the ink to make it usable. This is just my perspective alone.
[said while still in imminent danger from angry mobs]
If I do want to continue using a smudging ink, I usually use a piece of scrap paper, low quality copy paper, to be placed between Paper A and Paper B to shield B from the ink of A. Once you're fairly certain that the ink on Paper A is no longer hostile, then you can take out the shield paper and use it between the next pair of pages.
I've found that after some time this shield paper has a lot of ink marks on it and builds a lot of character, and is interesting to tag along with your writing, every time accumulating random ink marks.
As you use your pens and ink more, you'll start developing your own solutions to things, and your own unique preferences and you'll learn about qualities of various inks, nibs, papers and the combined effect of all three. It's just a learning process that everyone goes through, I'm still learning new things and I've been at it for the past 4 years.