The rapid growth of coins does not always indicate its success as the price may also fall rapidly. Therefore, it is better to let bitcoin grow slowly with falls and growth, but confidently.
You're definitely correct, some people think that the rapid growth of some coins or tokens is a good sign of a successful project but actually, it isn't because just what you have said growing slowly is the best sign of coin or token, slowly growing but surely rather than a rapid growth and also with quick falls and sometimes it doesn't rise anymore and get stuck at the dip. 
volume is the best answer, many altcoins find high performance but soon gradually weaken in less than a week, in the end they will face the fact that investors only take advantage of their coin trading and finally return to buy bitcoin. There must be a long experience to at least enter the top 50 coin markets.
Nah, those coins and tokens are just hyped by some people and investors that want a quick profit from their investments and all of a sudden they will dump it and it will surely crash. 
Even if the coin or token entered the top 50 in market capitalization there is still no assurance that it will stay there for a long period of time because anything can happen in this industry in a short period of time.