Not necessarily.
Every game has a luck component, whether it be a hot shooting night, favorable officials calls, etc. If the teams are sufficiently close in overall strength and there's an overly large luck component (rare but not impossible), then upsets happen. In WCBB there is traditionally a pretty large gap between 1 & 8, so the luck required is quite high. In MCBB, it's much closer so there are more upsets. If the gap is shrinking in WCBB -- and certainly with no dominant team this year, it's probably smaller than past years -- then an 8 could win.