This seems to be a recurring theme - that unless it's spelled out in ways that make it hard for the DM to "screw the player", people should be concerned about DMs screwing players. In this case, by selecting a CR 1/4 creature instead of a CR 1 creature.
5e is built on an assumption your DM isn't looking to screw the players. If it's a paramount concern for someone, 5e may not be the game for that person. If it's an ongoing fear, fixing this thing won't alleviate the general sense of DMs trying to screw players. If a person doesn't have a trust relationship with their DM, then that's what needs to be focused on, and not these kinds of rules. This version of the game is not going to change from a basic assumption that the DM has a lot more authority, will make judgement calls, those judgement calls will impact players, and a person needs to have mutual trust between the players and DM for the game to function well. No amount of tweaking precise wording will fix that issue, for this version of the game.
Specifically for spells, conjurations (due to their nature) just require more trust in the DM than evocations. Similarly, illusions require more trust in DM than evocations, and so do divinations. It's just something that comes with some classes of spells. It's not a bad thing, it's just a thing.