Good question, and I agree that there are plenty of passives that leave something to be desired.
Regarding your examples:
Some of the champs you mentioned have also been singled out internally and gotten some experimentation (like Heimer, Shyv, and Syndra), though I can't speak to how they are prioritized among other projects in terms of urgency and which ones are planning to move forward (within our team specifically, the only one that springs to mind is Syndra, though no promises on exact ship date atm hah).
Regarding passive quantity:
This is a controversial topic, but I wanna just share a bit of context here. It's important to keep in mind that we don't design passives in a vacuum and then decide how many each champion gets. Passives are designed to serve the needs of a particular champion.
Say I'm a champion designer making a new kit, and I start with a particular gameplay loop that fits nicely on Q W and E slots. The kit is somewhat functional and unique, but there are still things to figure out (let's say the W and E have some usability issues, certain lane matchups are very one-sided, my abilities late-game are confusing team mates, my spell rotation feels too unreliable, wave clearing is too easy, and my build paths don't scale right). What I do with the Passive and R slots--indeed, what I do with **all **slots--are going to be about problems like these or addressing other higher levels goals (like delivering the fantasy better or more unique or something).
The answer to those problems might involve any number of changes, possibly demanding 0, 1, or 2+ passives. If I do add 2+ passives, it's **not **because I just want the champ to be cooler or have more stuff than others. And it is going to come at the cost of power budget and complexity budget, not just added on top of an otherwise finished, balanced champion. A solution might even involve removing/nerfing passives so that we have more complexity and power budget to put on actives!
In the end, individual slots are not supposed to be balanced between each other, nor are "my champ passive(s)" vs "your champ passive(s)." Entire kits are supposed to be balanced between each other. "2 passives > 1 passive" doesn't always follow. It's very possible to design a kit with high agency, complexity, and fun with just actives, and it's also very possible to design a super lame kit that has several passives! And it's those kinds of properties (agency, fun, complexity, clarity, etc.) that we care most about: if a champion's multiple passives leaves them with too much control over the game, or too much complexity, or something like that, that is a big concern for us (and we definitely aren't perfect about these things!). But the actual quantity is usually not inherently good or bad.
Regarding passive quality:
Lemme give a different example: say we have a high-complexity champion who has everything BUT the passive slot locked down (you might have even had an awesome passive during development but it ended up being extraneous as other slots developed further). As in, "if our game hadn't already set the precedent, I might actually give this champ 0 passives." This can be a tricky spot: players expect each of their slots to feel fun and distinct, including the passive slot, but you don't want to disrupt the balance and fun of your existing pattern/slots.
A lot of these passives end up being lower-budget passives: we could have made Jayce get multiple intricate passives, but he's already so complicated and multi-faceted that it would probably detract from the kit to do so. Sometimes you make the call, "this champ is about these cool actives, and we should avoid detracting from that here."
This isn't to say that "lame passives" are a good thing, but sometimes the cost-benefit of trying to discover a perfect passive is outweighed by the value of delivering the champion to players with a not-stellar passive. The opposite is also true: sometimes we have a champion that's bloated in complexity/abilities by the time we're reading to ship, but we're willing to make the trade-off for the sake of delivering what we feel is a good product to players.
All that said, improving lame slots is definitely on our radar; I just wanted to give context. I hope that provides a little clarity for why passives compare/contrast in the way they do!