Lightning has also disadvantages, which are accentuated with higher volume (possible hub exit scam with massive channel-closing, opening/closing bottlenecks etc.).
This doesn't exist, there is no "exit-scam" attack. If a hub closed channels, everyone gets their money by definition, that's what channel closing means
It's also better to have a system with different layers with different characteristics, not only one additional layer, so if something goes wrong with one of them we haven't to fallback to on-chain tx alone.
Sidechains aren't a different layer, as they don't use mainchain scripts as building blocks
The attractiveness of sidechains, for me, lie in the fact that the simple and effective blockchain transaction paradigm is preserved,
Adding extra transaction chains doesn't preserve the simplicity of the blockchain paradigm at all, it complicates it. Using Lightning, of course, does not complicate the way the blockchain functions, because it actually is a layer on top of the blockchain
while LN introduces a whole set of new paradigms and some new centralization risks.
Right, the Lightning paradigm is a new paradigm (there's only 1 though, you accidentally made it sound more complicated than it really is). And as for centralisation risks, I think the Lightning devs have got that taken care of with the cyclic routing concept.
Additionally, once a sidechain is created and a lot of value was transferred to it, it almost doesn't need to interfere with the main chain anymore
Lightning just uses time locked transactions to expand capacity. There is no "interfering" with the mainchain, everything Lightning does can be done legitimately on-chain.
while with LN, opening/closing transactions would be relatively frequent.
This is... a mistruth that Lightning critics often use? Are you one such critic, d5000? There's no reason to close Lightning channels once most people are using it, why pay 500 satoshi fee when you can pay a 0.0001 satoshi fee?
(The two-way-peg in sidechains wouldn't be used very frequently - but it must work as a possibility so the peg holds.)
What if the sidechain pulls an "exit scam", lol
Sorry d5000, sidechains can work for non-BTC assets secured by Bitcoin miners. But no-one else in the cryptocurrency development field thinks they provide anything meaningful to help transaction scaling, oh, except the Drivechain devs, who go on and on about it every chance they get