It's all relative I guess, the TF is very different to an MX-5, and I think they are both good in their own right, it depends on what you want.
For example, if you want to hustle an MX-5 around a small roundabout at full attack, it's a great feeling of control when you have the arse end slightly sideways and you are progressively feeding the power to get as much traction out the roundabout as you can.. But do the same in an MGTF and it's totally different, it has massive rear grip, and you can really get the power down exceedingly well, with it almost slingshotting you out the roundabout with little understeer etc..
Very different, with much less drama, but still entertaining, just in a different way.
I don't quite get the term 'terrible'? in what way is it so deficient as to be deemed terrible? I have been on several track days in an MX-5 and with a mate in an MGF Trophy, and quite frankly on track, although quite different, lap times where quite similar, and in no way did I not enjoy the time in the MGF, it handled reasonably tidily, good turn in, little body roll, the only initial learning I had to do was getting to grips with the MG's rear end grip, but that's technique to a large extent, and the 160 engine once loosened up is more willing then the MX. I've also driven my brothers MGTF at a fair lick, and despite feeling more refined with less feel, it was still a hoot.. Then again, I have no real complaints about the MX-5, on track and on the limit it's entertaining, it's nicely balanced, if a little soft, but I couldn't ever come to the conclusion it was a million times better then a F/TF (160 variants).. Although my 'performance and handling' criteria is usually down to laptimes etc..