selens are easily dealt with because they're mostly effective in the first 2 minutes and its easily countered by 1 t1 tank which is worth 30 mass, also once u spot it (which is actually easy unlike you said) once it has nowhere to go because it has paper hp, as for subs u need to iinvest in t2 air hq + t2 torp, you need to actively search for it because it can actually move from 1 mex to other mex without dying unlike a selen, and on 20x20 maps where underwater mexes are often present it takes 1-2 min from 1 engi to move from 1 mex to another while on most 5x5/10x10 it takes 10-20 secs for an engi to build the mex after the prev engi died