Equal chance per here:
Which was right after summoning stones changed to the 8 specific troop per week style, and there were no (announced) changes to summoning stones drop rates (to my knowledge) since. This probably should be explained in game (if it is accurate).
As for the others:
Pet baskets aren’t technically (directly) monetized because they have a gameplay gate between the thing that you buy and your prize, so you are techincally buying the ability to do the thing and not the thing that gives you a (random) prize. If we are counting those, we also don’t have any official rates for specific orbs from chaos orbs (monetized through gem buy ins through events, gems are directly monetized), everything that comes out of a vault key (monetized through selling of vault keys and/or events, through gems), the ratios of the various delve chest drops (monetized through delve events, through gems). Add that on to hidden mechanics, such as drop rate for the current troop in the glory pack being heavily skewed to dropping that troop if that rarity is rolled when using an event key (not explained anywhere in-game). For things that aren’t monetized in any direct way but still might inform player decisions (technically it can be argued that nearly anything in the game can be used as a motivator to get someone to spend to get a tool to be able to get their prize either more quickly, or at all but these would be roundabout at best as opposed to the one-layer of abstraction noted above) traitstone drop rates in both explore and PvP (a few rarities were briefly touched on, on a dev QA stream, one time, with a promise to share them all on the forums, which never happened), token drop rates in explore (we have mostly accepted drop rates found only from digging through game files posted on the forums, no official confirmation), ingot drop rates in PvP, adventure board appearance ratios (both task type and rarity), gnome appearance rate, full gnome drop tables and ratios, full legendary task drop tables, the actual chance to get a given prize when watching an ad, and probably some other stuff I’m forgetting.
Yeah, there is a lot of room for improvement in this department.