It would be used less more and also be less more successful because the bitcoin is also became popular because of the altcoins
No, those alt coins doesn't even have something to do for bitcoins success. Bitcoin became successful all of the sudden when those early adopters found out that it can used as a medium of transactions. And those alt coins that came out just copy cat the idea of bitcoin because many developers saw the potential of crypto currency which bitcoin is the original source of it.
Wrong. Altcoin's company has introduced a lot of people to bitcoins. Without them, bitcoin wouldn't be as successful as it is right now. I know that altcoins are just a copy of bitcoins and people mainly just use altcoins to earn even more bitcoins, but that's okay. The gist is that every new member of the altcoin community is eventually a new member of the bitcoin community. The introduction of altcoins is one of the key to reach mass adoption. I've never seen someone promoting bitcoins but I've seen tons of people promoting a certain altcoin.
Bitcoin might already have become recognized even without altcoins but that recognition wouldn't push forward if it wasn't because of the help of altcoins. The bitcoin success would be much slower without altcoins.
In that case I would like you to counter my opinion, why I believe altcoins are useless except for trading purpose:
Altcoins of turn out to be stagnant, non-changing in price in other words "dead" and left by developers until a fork is delivered by some other developer. They also turn out to be scam projects at times.
Now many people have been introduced to bitcoin after altcoin promotions - just like you said in your message - then they have a first preference to the altcoin than bitcoin - next the altcoin turn dead or scam. The investors now think bitcoin to also be a scam project and brand it as scam too.
This may not seem realistic but has happened in many local communities where people were promoting altcoins, one of which I was once a part of.
I can see the discussion here but i would say that altcoin help Bitcoin a lot in terms of New users being introduced to bitcoin. I also believe that altcoin are not used only for trading or so we say useful. But instead altcoin are somehow a testing grounds for some possible update to bitcoin in terms of application with regards to masses' reaction.