There are two opinions on TD's:
1. People don't know how to use them and cry about getting owned.
2. People that look at the stats and know that something isn't quite right.
I fall into the latter category. Compared to tanks TD's have the same if not weaker guns, weaker armor, less mobility, more restricted view ranges, and are hideously expensive(esp the Ruskies) compared to the equivalent level of tank.
The very slight accuracy bonus just doesn't cut it against the major negatives, which almost seem to get worse as you get up the tree.
Yes you can do well, on certain maps and certain makeups, but if you deviate from that you're going to have a tough time. Especially in T3/4, you can't do any serious damage to anyone but light tanks and will get SPG'd if you reveal. Some of the maps just don't have a lot of good spots. Plus most of the tanks you will encounter can out range you.