Would be nice actually. The MIG 21SMT can carry more fuel because it was built for that purpose with additionnal fuel on the back of the plane. With larger maps being way more popular now than before, i think every jet need to be able to mount external pod (if those existed for the plane).
Well i carry 30 mins, but on larger maps when the last enemy is running away, having to go back to base instead of catching up is really annoying. So on those map to be really comfortable i usually take the max amount.
but on a serious note, the only quality i found mig 21 SMT to have is its climb rate and top speed… turn rate and pull dont amuse me very much… for a delta wing aircarft