A resolution mechanic is just a way of generating a value along a certain numeric distribution that has certain statistical percentages associated with every value. How you present that is up to you, but in the end, math is math. A d20 is just a percentile system broken up into 5% chunks. A d100+value vs. target number system is just a percentile system in reverse. a 2d6 or 3d6 or 2d10 mechanic is just a bell curve along a 1% to 100% statistical distribution, but all the possible values can be placed along the line.

Ultimately, it’s all a matter of personal preference. If I use a 1d20-roll under mechanic for ability checks but percentile dice for Thief skills, but my thief skills are all broken down into 5% blocks, mechanically there is absolutely no difference.

Now, granted, I think there might be an argument for having more than one resolution mechanic for things that are not necessarily character-based resolutions. For example, you might have a d100+value vs. target number system as your main mechanic, but still like the idea that for initiative, you just have everyone roll a d10 and highest goes first. Or just have a sliding 1d6 chance of something happening while on the road while traveling.

I guess what it comes down to is, resolution mechanics are all, in the end, representations of probability. Determine how you want to represent probability of success in your game, and go with it. If you feel that not all probability mechanics should be linear, then use a bell curve. If you think having “mini-games” best fits the feel of your RPG, then go for it. As long as it all makes sense, doesn’t feel arbitrary, and is clearly explained with appropriate examples, you should be good to go.