The TDF is in no sense as powerful a force in the 3050s as it was in the 2600s. Other than their willingness to go instasun, as one admirer of them puts it, they're not really any more powerful militarily than the FRR.
Lets put things in perspective.
The TDF wasn't anywhere near as powerful as the SLDF in 2575- but they managed to hold their own far longer then expected.
The TDF/periphery rebels weren't anywhere near as powerful as the SLDF but they managed to destroy a huge number of SLDF units.
The Smoke Jaguar's are no where near as powerful as the SLDF. Any single army in the SLDF was numerically superior to several clans. (For example the 7th Army - one of the smaller armies could count 61 mech regiments in it's TO&E). So sure the TDF is not what it was prior to the reunification war, but the clans (numerically) are not the SLDF. And technologically- well I never said the TDF would win in a straight up fight- they're going to win by destroying the Clans transportation and support capabilities.
Another factor to consider is the organization of the TDF- the TDF as it's name implies is a DEFENSE force, not an offensive army. The bulk of it's forces are armored units and infantry- each planet has at least a battalion of armor and many worlds can deploy entire brigades. During the Reunification War it was these armored and infantry forces that held off the SLDF for so many years- the battlemech forces were largely held in reserve for counter attacks and such. (See periphery 1e- for example-on Ridgebrook the 2nd & 15th fortress battalions which lacked battlemechs, held off elements of 2 divisions for 4 months). Yes the TDF has been pretty poor during the Jihad in it's campaign to liberate the Pleiades but that's because it's fighting out of it's element- on the defensive, fighting from prepared positions, with guerrilla tactics, etc the TDF is going to be a lot tougher.
