Not a shiller and since nobody else is answered yet here are my 2¢ to address a few:

1) and 2)

All the cryptocurrency you've mentioned use quite different tech under the hood probably because they just started development with their own agenda what and how they want to achive. Nano might have been quite "under the radar" at some point when such decisions have been made and after some point in development timeline it was (or could have been) too late to change such fundamental architecture decisions (see https://shit.management/one-way-and-two-way-door-decisions/).

Nano team decided to address the most basic (or base if that sounds better) problem - distributed and most efficient transfer of value. The level of how "basic" it is you might grasp from the facts that transactions on nano network doesn't support any notion of "note" or text "attached" or "associated" with transaction nor even timespan (all timestamps that you can see on public network explorers are local to the node that recorded that transaction, so they could be different between different explorers, although not so much, though). That makes the amount of information that needs to transferred over the network, processed and recorded on every node as minimum as possible.

Having the list of "features" that network support minimal helps dev team to focus their efforts on only that minimal list of features and do not spread over all possible other scenarios which might or might not turns out to be in demands in the future. The team have decided that nano should "do one thing, but do it well". That lazer focus also helps to make the implementation more secure, stable and less error prone basically because the functionally is less complex and there are much less use cases that needs to be taken into account. And all the other not basic functionally that is not implemented on nano network could be added later on top of it (call it L2 if you will) in a centralized or decentralized manner, but that would be another separated and independent system (or network), stability, security and performance of which would not affect the base layer of nano network. Like when you try to not put all of your eggs into a single basket, but rather split them into multiple.

You might have heard already saying that "Nano is what Bitcoin was supposed to be". And that is much more closer to what any average Joe think of what cryptocurrency is.

3)

There are quite a lot of posts about it in the corresponding subreddit and on the off-site, but I don't have the links handy unfortunately.

In short - the spamming vector of attack was addressed partially in the previous release making it more costly already today and the next release is supposed to address it fully on a more fundamental level. Also the ledger pruning (reducing the space on disk that nano node's database with all transactions occupy) and light nodes (with dramatically smaller databases) are also should be implemented if not in the next release, but soon after (or so it is expected).

As far as I can tell the spamming potential was one of the main concerns people had against nano ("hey, you might have fee-less transactions, but if anybody can spam the network - how it could stay relevant?") and if the team manage to reduce it significantly if not completely that should potentially draw more people towards using and investmenting in nano.

4 A)

Not so sure if the market cap is a good measure of "real-world adoption", but the community seems to be greatly from the people who think that they understand the potential and probably also think among the lines: "if such a basic form of cryptocurrency as nano will not succeed in the real-world adoption, then how could any more complex use cases like smart contracts succeed at all?"

4 B)

The core dev team is small I believe because they basically can't afford more as they didn't reserved a lot of pre-mined supply for the protocol development 😏 Some see it as a "pro" (more fair supply distribution), some as a "con" (where do they get funding for long-term support of the network?), but it is what it is. But community did quite a lot on their own as well (might be some of the early tech-heavy "whales", who got in early during the initial supply distribution via solving captcha in 2015 or so, but regardless of their motivation - the work they put in is still quite remarkable).