All altcoins are by nature, just copycat, pump and dump coins. Pump the price a few points, gone tomorrow. Gimmicky features, gimmicky logos, proof of stake 10%, oooh 10 second confirmation times must be good!
That's a very sweeping generalisation that does no justice to the complexity of the altcoin market.
First - there are 2 very different contexts in which bitcoin can be appraised:
[1] - monetary context
[2] - technology context
In other words, in a monetary context bitcoin can be perfect (meet all the requirements for high quality monetary medium - like gold does) but in a technology context it may not be (like gold isn't:not very portable and not very transmittable).
Even in a monetary context, however, bitcoin has 1 missing property: fungibility. The fact that coins can be tracked on the blockchain detracts from bitcoin's suitability as a monetary medium by adversely impacting on its fungibility. Several altcoins address this deficiency directly and there is no sense in which that feature can be described as a "gimmick". It is a fundamental property of sound money and the market will endorse that fact.
Secondly, although bitcoin's deficiencies in a technological context may not detract from its marketcap or monetary suitability, they will detract from its useability. There are all kinds of areas where this is true. Take, for example, the "shares" based algos where shorts in pegged digital assets are matched against a natural demand for stable currencies for use in retail. This is a fundamental monetary mechanism which has been in use in societies for eons. Despite that, there's no way bitcoin itself will ever meet that market requirement, it's a completely different monetary animal.
Nor are sidechains ever likely to meet these requirements because the idea isn't remotely scaleable enough for the reasons I outlined
here (and even if it was it wouldn't address the demand for genuinely de-coupled alt currencies).
In my opinion, many alt coins haven't even approached 10% of their potential value against bitcoin. Some of them could well exceed Bitcoin in marketcap even if BTC remains the cryto "reserve".
We won't know until adoption takes off because while there's no widespread adoption the altcoin's technological advantage is redundant and speculative only.
With widespread adoption however, there we'll see entire markets for which Bitcoin simply isn't suitable for practical reasons - too slow, too precious, too transparent, too whatever. At that point, I expect that some of the alts will rocket in value to fill the gaps.