If a node guessed it was the full amount passing thru it would be right most of the time. If many transactions are passing through large hubs (because they are well connected and require less hops to the destination = more likely to succeed and cheaper) an adversary could collect quite a lot of info on the network. But sure it existing gives some plausible deniability. If it was made default that would be even better.

>"Monero also requires trusting that the other 14 keys are not held by the same entity or cooperate to deanon you."

You mean 15 decoys? That only applies to senders and every spend exponentially decreases the likelihood of being denon'd. Also, you don't have to trust others not being the same entity/colluding for reciever or amount privacy on Monero (both technically possible with LN if the nodes on your routes are colluding, but very unlikely)

>"This is true for any privacy system and impossible to avoid."

It's not true. Cryptographic accumulators are not really affected by the problem you describe because you're proving you're one of the global set of all transactions instead of a tiny subset - which is what will FCMP be.

I've been around many different Monero communities/forums/groups for years and I've never heard Coinomi before. Not sure who recommended it to you but that is not the norm at all. It's usually Cake, Monerujo, Feather, or the GUI/CLI.

Yes, scanning can be annoying, but that is what guarantees no one but you can see your transactions (any proper LN privacy wallet, like Zeus, also requires scanning). If you use it somewhat often it's not really a big deal. Wallets with periodic background scanning make this a non-problem. You are always caught up (or very close). You should check it out on Cakes new update. It's very new so I'm sure in time more wallets will adopt it.

The only Monero wallet left that holds users viewkeys to eliminate sync time, at the cost of some privacy, is Exodus I believe. There used to be another one MyMonero but it's been defunct for quite a long time.

Block filters only help privacy when querying, not when broadcasting a transaction.

Not sure what you meant by the last part. Generally more people using something means a larger anonymity set.

I've grown to appreciate Lightning more, but there are a lot of nuances to both. We could talk about them forever.