"can and should" is a personal opinion that not everyone shares. Should my preferences have to affect everyone's game by being in the base rules, can be level at each side of this debate, so it's not really helpful, especially if something else you say might be construed as a personal attack.
The irony about ability score increases in 3e and 5e is that you'd think with bounded accuracy what doesn't work in 3e actually might in 5e, a +5 modification in 3e is just one of half a dozen modifiers you're putting in, but 5e was designed around tamping down that kind of power creep, I hope the designers tried to work around it more with the revision.
