As the S&P 500 and Nasdaq 100 indices continue to notch new all-time highs, it's clear that the rising tide has not lifted all boats.

Sharp-eyed analysts and investors have noted some discordant features in a stock market at its peak, raising questions about the euphoria that currently reigns supreme on Wall Street.

Mega-Cap Dominance Unprecedented Since Late 2008

The dominance of mega-cap stocks hasn't been this pronounced in nearly sixteen years.

The top 100 U.S. stocks by market capitalization, monitored through theiShares S&P 100 ETF (NYSE:OEF), have never been stronger against the Russell...