choose puzzle type

That would require first of all that themes are assigned by experts and AI-systems and not by common members as now is the case. Many of the keywords make no sense whatsoever. For instance, many puzzles have a passed pawn somewhere which plays no role in the solution but still shows up as a keyword.

Emphasizing requested themes has the disadvantage that the solver is prepared to look for those which is unreal in game situations. Part of the solving skill is precisely to detect the pattern of a promising tactic.

I would advocate the opposite approach. Many puzzles are solved only because the solvers know there is a solution. Much more real would be to spice the puzzles up with positions where no tactic works or where the tactic is set up as a trap. They are simply unsolvable - just as there is no guarantee there is a winning combination in your game even when it looks promising. The correct answer would then be to tick the "no solution" box!