Geez, this is a shocking post.
If your wicketkeeper is not Kamran Akmal. Level incompetent you should always go with the better batsman.
A mediocre wicketkeeper drops at max 1 chance per match.
Now there are eleven batsman in the opposition, if you drop a catch of a no. 8,9,10,11 batsman 99% of the times it won't cost you much TBF even dropping a no. 1 to no. 7 bat will only cost you 50% of the time at best.
Combine this with the probability that the catch is dropped while your team is well on its way to victory
Dont stop here, combine all these with the fact that even great keeper drops 0.3 catches per match.
So basically it doesn't make as much impact while we just saw that how a competent batsman wicketkeeper can win you matches.
Foakes was brilliant in the last match, still dropped two, Buttler has dropped 2 catches since 2018 and he has played in a variety of conditions. Now everyone who saw him know Foakes is better at wicketkeeping but does it really make that much impact?
If your wicketkeeper is Kamran Akmal level incompetent then go ahead select a specialist keeper but if you have someone who keeps like Andy flower but is a match winner with the bat go for him. As simple as that.