This question has got me thinking of the possibility we could have been enjoying if there is nothing like the Ethereum blockchain that gave possibilities to the development of all the other chains in the crypto space today,
You are mistaken if you are thinking Ethereum is the first ever coin that was created as an alternative to Bitcoin. There was Namecoin, Litecoin, and Dogecoin among other chains that was developed prior to 2015.
I know one of the advantages of the ethereum blockchain is the fact that it gives room for scalability and possibilities of getting services that the Bitcoin blockchain may lack.
The advantage on scalability maybe true before but this is not the case right now. Ethereum is more congested and it costs more to send ETH than BTC today using p2p method.
But another setback is the adoption level since the ethereum blockchain gave birth to several cryptocurrencies it makes it hard for mainstream recognition of a single crypto coin
You cannot fault the birth of Ethereum and the increase in competition for the lack of mainstream adoption of any coin. Do not expect every coin to be recognized in the mainstream as some of them are not really designed for it. Take Monero for an example.
which was the original intention of bitcoin.
Can you point to us where in the bitcoin whitepaper does it say about mainstream recognition? I only know it was meant as an alternative payment system where you and I can send money peer-to-peer.