The too much bit for me is the head angle, weight and the position on the bike. A ponderously slack head angle is not a good thing in the lower speed twisty flatter sections and a position on the bike with bars above your saddle and generally rather sat up stance is not going to help you move around an xc route particularly well or up hills particularly quickly. You obviously don’t want to carry around any more weight than necessary too but you can look at your waist line as much as your bike for that!
If the bike in question does not fail on the above does it really matter too much if you only use half or 2/3rds of the available travel whilst mincing around an xc route? Obviously when you see what the xc race boys can get around at speed with a steep head angled hardtail and 80mm forks a 140mm full suss is more than needed in the strictest sense of the word, but if it is going to ruin your fun is a question only you can answer. 100mm front and back is a good compromise.