Bitcoin's dominance (coinmarketcap.com) is at an all time low now - 33%
I am also worried about the same. It was around 39% just two days back. However, if you are monitoring bitcoin constantly, you have noticed that the price has recovered from 13,000 level to 15,000 level even after loosing the market dominance.
Bitcoin transactions are slow and expensive. Other altcoins offer much better features.
People are slowly moving money from Bitcoin to altcoins.
I totally agree with you on this. The network traffic isn't coming down to an optimum level where the network can support that resulting in high transaction fees. The current transaction fees is not practical for smaller transactions at all. A lot of people including me started investing in various other cryptos now.
Is bitcoin losing its relevance?
People say Bitcoin can still be used as store of value, but is there any value in an asset if it has no utility?
Probably no. If you are aware of the current news then you must know that lightening network is currently being tested in testnet. The first transaction using this LN was super successful where the transaction was instant with no fees. Within the first quarter of 2018, it is expected to be implemented. So just stick with bitcoin. Good news are on the way.