Microwave "safe" just means that the plastic will not melt from the actual RF from the Microwave and are made from "food safe plastic".
Pitting is normal when using plastic in a microwave, comes from the uneven heating of the food and cannot be helped.
Foods with high fat/grease content tend to cause more pitting than foods with lower fat content. Foods with tomato sauce bases tends to add extra insult by leaving a orange stain behind that is impossible to remove.
With plastic containers you just need to replace them when the pitting gets excessive and is hard to get clean.
As far as chemicals leaching, yeah, I am sure plastic does leach some but like I mentioned, the plastic must be food safe which means what does leach is supposed to be non toxic and at very low levels.
If plastic leaching is of a major concern then like others have mentioned, change to items made from Pyrex Glass. Corel dishware is made from Pyrex glass, is durable and light weight. Very low cost and easy to find and works great in a microwave..
As always, with any glassware, make sure there is no gold or silver decorations embedded in the patterns or around the edges of the plates and bowls.. Should be pretty safe with Corel, but other manufacturers you might still find some with fancy gold or silver accents.