I know you said "at least"- but back in 1998 you had some crap teams like UK, and Georgia and some below average teams like Vandy. Now, I don't think that there are any programs that are bad- yes some are down like MSU and Georgia, but those are also programs that could easily be back in a couple of years if not sooner.
Let's be honest here- they had to change the regional format in part because too many SEC teams were getting in. One year, there were five teams in- I think in 1997. Over half the field!
I know it's cliche, but I do think that the SEC Tournament is tougher than the CWS most years mainly because it is more condensed and it forces you to go through your staff more quickly. Also, the NCAA usually has it set up so that some mid-major like a Cal-Irvine makes it through, and that makes the CWS field slightly weaker.
Also, you look at the top 100 college draft prospects, and I think something like 25-30 are SEC guys. I would suspect that's pretty typical for the SEC, and that's just the juniors and seniors. That's not including the other 20-25 or so sophomores and 20-25 or so freshmen in the league. So, you do the math and you see that of the 156 "starting" players- I'm including the three weekend starters, the closer, and the DH as well as the other traditional positions- and you get an estimate of about 60-75 players in the SEC are legit high draft prospects. All of these numbers are estimates and may be totally way off, but even if it's something like 40 players in the league that end up being top 100 prospects of those 156 guys, that's still a ton for a college league.
In all honesty, you can go to Starkville or Oxford and see about as many MLB prospects as you can in Pearl.