If the Bucs had beaten the Bears, the Bears wouldn't be a playoff team, so the Bucs wouldn't get credit for beating a playoff team.
If the Bucs had lost to the Vikings, then the Vikings might have been a playoff team at 8-8, so again a win over that team gets no credit but a loss would have made them 0-1.
If the Bucs had lost to the Giants, the Giants would be a playoff team too.
The Bucs beat the Raiders, who had the same record as the "playoff team" Bears.
If the Bucs had lost to the Chargers, the Chargers would have been 8-8, same record as the Bears. Hence, one team, the Chargers, suck while the other team, the Bears, are "a playoff team!!!" The only difference in their records: the Bucs beat one and lost to the other. That is, if the Bucs had instead beaten the Bears and lost to the Chargers, the Chargers would be 8-8 with the same record as the "playoff!!!" Bears while the Bears would be a 7-9 team that "sucks" and the Bucs win wouldn't mean anything. See how that paradox works?
Simplifying your fallacious reasoning...take out the Bucs outcome itself, and look at the following team records:
Bears, 8-7
Raiders, 8-7
Vikings, 7-8
Chargers, 7-8
Against these four ~.500 teams, the Bucs went 3-1 with a plus-10 ppg differential. Of course, the only game that shows up in your argument is the one-point loss to the Bears, which is then reduced to "0-1 against playoff teams!!!" That's the problem with using a small sample size like this...it's mostly just randomness and bias and is reduced to absurdity. It's not much different from people complaining the Patriots schedule was so easy for so many years because you could mark down their opponents going 3-13 against the Patriots. The reasoning is like trying to pull your chair out while sitting down on it.
The Bucs played three elite teams this year, teams that are outside of the muddled middle of the NFL: the Chiefs, Saints, and Packers. They manhandled the Packers, lost to the Chiefs by 3, and got their asses kicked twice by the Saints (second game was a lot more of a problem than the first one.) They're a team on the rise that got whipped by some teams that have been elite for years and have MVP caliber QBs.
Not unexpected when virtually every analyst said they'd have growing pains this year.