So, just to be clear... Fallen suggested that for smites, the solution might be to have the option to toggle the smite on, that you'd have to select and toggle from a choice of multiple different toggle options that are all visible on your screen independently (smite level), to activate if you hit - something that you would need to deliberately do before hand, before attacking, and then need to toggle off again after you swing your weapon, so that you don't continue to burn spell slots every weapon swing... And they are suggesting that that is a better way and preserves combat flow and speed more than having an automated question come up when you hit where you can click once, in a pause that takes less than a second, to choose whether to smite and what level if so (can be done with one click, and certainly in the solasta implementation, the reaction pop-ups are usually on screen for less than a second and do not, in fact, slow down combat in any tangible way at all, compared to the time it takes to just straight up make your move or make a decision about how to react on your turn). That's what it sounds like they're saying here. Is that what they're saying?
So you know, Fallen, since you seem to be making many broad assumptions about 5e rules without actually knowing (please don't do that - do your research first, it helps everyone): no, you do not get more reactions per turn as you level up; you only ever have one, whether you're level one or level twenty.
If deciding whether to cast shield or not when attacked causes your friend a decision gate which takes them twenty extra minutes to resolve, that's entirely on your friend and nothing to do with the game. You likely spend longer on your own turn moving barrels around and shimmying your character carefully around the enemy to ensure that the auto-path AI doesn't proc an unnecessary OA on you. Exaggerating to extreme values does not serve to enhance your argument - it actually weakens it, because it demonstrates that you need to push to extremes and treat them as normal just to make your stance look tenable... which is usually an indication that it's not.