1.No ideally.but please check if ur no. of re-transmissions is high for higher MCS.Also check what is your initial MCS for transmitting the first TBF.It shouldn’t be higher than MCS-5
2.Same as the reason of TCH Drop along with TBF congestion & frequent LU & Cell reselection.
3.General formula for TESR=Total successful TBF establishments/Total TBF establishment attempts.
Actually error protection bits are lesser for higher MCS,so re-transmissions are usually higher and drop rate is usually higher,this is actually a trade off between throughput & drop rate.For cells with good Um interface quality, the Link adaptation mode is usually used. For cells with bad Um interface quality, the Incremental redundancy mode is usually used.