Boros has some crazy feats like, tanking casual punches (which is a big achievement when said casual punches could instantly kill mountain-sized monsters), matching Saitama in speed and melee, sending him crashing in the mount great speed and all, and some pretty crazy regeneration feats (pull himself together seconds after Saitama blows all but his eye away). Also, he has a surface/planet busting attack (depends on translation). Madara would basically be fighting a 8th gated Guy but with regeneration and no time out (unless he use Meteoric Burst).
Madara has hax tho, and hax tends to outstrip raw power in most cases. Immortality will also helps him survive the planet busting, even if he'll probably be nothing but some sentient pieces scattered amongst the floating ruins of the planet.
So Boros wouldn't defeat Madara, unless you think the immortality was an hyperbole or take it out of the game. He'd give him a tough fight though, enough for Madara to go into his ham mode and start complimenting Boros.