Even in that case it doesn't make any sense as teams can carry over salary cap space they didn't use during a season into the next one.
Yes, the carry-over aspect is often overlooked. There are two key considerations here.
The obvious one is that what you don't use now can be used later; this was not true under the old CBA. Thinking about this year without at least looking at next year is putting your head in the sand.
The less obvious one is the bind created in future years, as soon as the following year, if you spend up to the inflated cap limit with multi-year contracts. Using that additional $10 mil on contracts with signing bonus cap hangovers in future years is a must-win-now strategy. I wouldn't expect to see that unless TT thought his job was on the line. We're not there yet. Yet there is a faint smell of recognition in the air that on balance this is not a very good football team once you get past Rodgers, so lets say TT gets somewhat agressive and uses $4.4 of the $9.4 mil in carryover this year.
That takes the $28 mil available cap down to $23 mil.
Also, the reported $28 mil cap only accounts for the top 51 at this moment. Once the season starts, the 53 man roster + practice squad + IR + PUP counts against the cap. If you end up with 10 guys on PUP and IR and add 2 guys to the 53 man roster and all 12 of those guys were merely minimum salary rookies, you'd need to have $5 mil in reserve. Practice Squad is another $1 million.
Now we're at $17 mil in available cap.
You also need to sign your draftees. The top draft picks are most likely to bump minimum salary guys off the squad and out of the cap hit. Figure on $2.5 mil cap hit in the differential.
Now we're $14.5 mil in available cap before signing any FA, our own or an outsider.
Suddenly, the expansive riches in cap space are not so expansive.
This goes to illustrate how difficult it is to maintain a solid veteran presence while avoiding future dead cap hell or a season of slash/burn/rebuild. The key to extended years of success is drafting well and getting a lot of productivity out of players in their first 4 years when they are cheap...and have more young guys constantly come up behind them so there are options when the cycle of 2nd./3rd. contract extortion keeps rearing it's head.
It is very difficult to get around a few years of mediocre drafting. A few FA vets who won't cost a lot in signing bonus (read: potential future dead cap) is the only real stop gap available.