This is a definite exaggeration. Most open plains maps, even if they had hills, the cav could do very well and with all ranged gimped, limited slots so fewer pikes, and higher riding skills than pre-January they will tend to dominate. Every map in the end is a cav map with their OP stats right now. Town - turn fast corners with a couched lance, kill, and ride away before retaliation and repeat. Hilly - Ride behind the hill so cant be shot then turn the corner with couched lance, kill and ride away before retaliation. Full open plain - Wait till melee engaged and mass charge utterly decimating engaged enemy troops, then ride away with super-jet fueled coursers and repeat.
There was only 1 truly mountanous viullage map I wouldn't recommend cav (though I did see a few do okay) and that was Gisim up in the Northwest.
Siege is the only place where cav gets off their horse and thats why the recommended 1h/polearm riding combo with shield skill. Shielders will be even more useful now as fewer ladders (take up so many equipment slots) and not as easy to ladder spam. So just pull out pick and shield and you are good for a siege or use a xbow with 1 wpf on defense like half the teams will probably be doing as do so much damage without needing to wear light armor or have skills in it.
Main thing is don't go 2h/polearm- no shield, no riding. Very little need for those unless you are the absolute best or they are specifically hiring you as dedicated pikeman. Throwing right now is also a bad way to go.
You got some points, but you are also over exagerating. We are speaking about Strategus, not some random public matches. First, horses won't be +3 heirloomed in Strategus, and that means a lot for AirArabia JetPonies. Furthermore, they still cost a fuckload of money. Third, most horses go down in 3 arrows, less if they are heading towards the archer. Cav that try to go rampage turning around houses in a village map will be confronted to pikes and roofcamping archers. Even doing one kill is hard in that kind of situation. The couched lance is extremely risky. Even onehanders can take you down with correct timing.
In any village, an organised defensive force will camp roofs with as much archers as possible and put pikes on the sides, cav is basically nullified in those situations. Defensive cav can manage to get a few kills but will soon get shot by attacking archers or die trying to flank the infantry near the village.
The only possible spot for cavalry are battles on flat terrain. If the infantry clash actually happens before the battle is settled, then cav can be useful. But if it's not, mainly because of hilly terrain, then cav can just hope not to get shot. If both teams camp hills, whoever has the best ranged wins.