From my observation of some older traders who are consistently profitable in the market, I have observed that they usually are very consistent with their strategy or approach to the market.
Just as starting to trade on one pair first is important for a beginner trader, it is also necessary for a new trader to know that the easiest way to become confused is to try to learn different trading strategies from different traders or sources at once.
One trading strategy is enough to make you successful until it is no longer working.
I agreed to your opinion because having different trading pairs can put someone in a tight angle were it will be too hard for him or them to followup the trade as the market is waving, although this can depends on individuals because professional traders can have about more trading pairs, what I won't encourage is to trade on a newly launched altcoin as a newbies because they wouldn't know how to control and handle the market forces.