Again, application of knowledge is one of those action declaration things, where the GM adjudicates and may call for an INT check -- where the fighter's low INT will result in problems. The player knowing things doesn't always make them true, and, even if it does, you can trivially design around it. If you don't care if the player's know what the resistances of a creature are, then the low INT fighter's player knowing them doesn't matter. I tell my players these thing often, and it doesn't make for easier combats. I often give this kind of information out freely to PCs that have proficiencies, with no roll needed at all. To be honest, I'd find a way to tell them anyway, I just like leaning on proficiency because it's an ROI for that player's build choice. Doesn't make my game trivially easy.
If you remove the problem on the GM's side, then what the players do just doesn't matter. "Metagaming" is a GM created problem.
This isn't to say that if your table likes playing in a specific way that's usually characterized by "metagaming" that this is bad. It isn't. But, if it is a problem, then the problem is on the GM's side of the screen. If it isn't a problem, and everyone agrees, then it's absolutely the right way for that group to play. The only right way to play D&D is the way that is fun for all.