I can understand dumping the megadrive and going with a narrower cassette especially if the OP is using the bike on the road. If the local terrain doesn't call for very wide gearing, then the closer spacing of mid range gears which actually get used is a major improvement.

I try to set up my bikes so I do most of my riding in the sweet spot of the cassette where the percentage stems are smallest. That gives me them best selection of similar gears to adjust for slight grades, wind, or just an off day within the gear range that I use 80% of the time. Of course if the terrain called for it, I'd want a nice low low gear, but if not, it's just dead weight at the expense of usable gears.