I sort of agree, those guys would be nice additions to the team this year. But I'd say LB would still be a big need this year and most of those other positions would all still be needs next year, some even more so.
As a GM, you have to look out beyond this year and see what you will probably need next year and the year after that. You simply can't just plug and play most rookies at many positions in the NFL. They need a year (or more) to get where you need them to be.
So IMHO, that's why adding a good WR, CB and/or a DE this year is smart, even when there is a good chance they may not get as much playing time as you'd like from your top draft picks in year one. At least not if all goes to plan with the guys you already have on the roster. But if for whatever reason they aren't as great as you hoped or they aren't here after this year, as many of them might not be, you already have their replacements in house and they're ready to contribute much more than most rookies.