For the AEC part: the AEC gives you the dynamic the UKF opening lacks. Even if you are getting rushed by a Puma, as long as your AT units are positioned well, you should be able to get the AEC out or even better defeat the puma. Furhtermore, going for the upgrades and using the abilities is also the key to victory, considering all the awesome toys UKF gets with their doctrines and the advantages of five man IS using double bren.
In general, I have the feeling that people do not get the general concept of this game. Axis as a lategame faction should win in lategame (for all those KT is op guys). In the same manner SU and USF are strong during early to mid, therefore their tasks is it to defeat the opponent during the early game. UKF however, have a weak early with a strong mid and some highlights for the late game. So my advice would be not to create this boring monotony of similar faction and actually start playing around the strength and weaknesses of the five factions as well as using tactics.
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TL;DR
UKF needs to be played defensively first, needs to make use of cover and then use the fast tech to beat your opponent in the mid game.