Are these folks not still casting with less than the whole rod? So he sticks it back together. That only gives a bit more backbone for large fish. Banty 'boo rods are generally made by using the top 2 sections of a 3pc 8'-9' rod and people fish with those all the time. Same principle.
CCS measurements on a MHX 9' 4pc #5 blank that was handy here in the shop. For the whole rod followed by the top 3 sections only.
Using all 4 pcs, the rod has an ERN (Effective Rod Number) of 5.65. This translates to a heavy #5 that would certainly tend towards a #6 line close in. The Action Angle, which is indicative of the speed of the rod. is listed at 70 which just barely translates to a fast rod. It is faster than most blanks I have measured. The idea that MHX suggests effectively underlining this blank by about a half step would explain the fast feel to the blank.
Using the top 3 sections for the next set of measurements, I get an ERN of 5.65. Notice that this did not change. Pull it apart. It's still going to cast the same line. The AA did fall into the moderate to moderate fast range at about 67 so dropping the stiffer butt section did slow the rod down a tad. Overlining to a #6 will give this configuration a bit slower feel but would probably work better in close.
Putting it back together is more work than is necessary. Drop the reel in your pocket. All it's doing in this situation is storing line anyway.