This is the time when Security Control started to become more popular in tournaments. With the introduction of 2 hands of Omegamon, Supreme Cannon and Transcendent Sword, and a very good black option card Ultimate Flare, the security control profile stays at tier 1.5 max.
During BT5 Meta, Security Control is like a deck to show off Omega Zwart Defeat or BT5 Omegamon(s) since these are the most expensive cards in current meta. The Security control is strong over Lordknightmon deck if these cards are drawn early: Ultimate Flare, Surpeme Cannon and Alter-S. But to use many colors in 1 deck is another issue for card distribution, that is why people prefer Yellow & Red & Black Sec Con for recovery instead of Red & Blue & Black Sec Con.
For Lordkightmon deck, if you play against Sec Con, you should try to maintain a 4-security limit against SECCON (else, they will use Magnadramon to "recovery" when their security is at 3 or lower), and prepare a wide board using LordKnightmon. When doing swarm at their security with many Digimons, they will find it quite difficult to recover fast enough, and pray for the Ultimate Flare is not opened from their security.
Security Control moves up to Tier-1 when the Atomic Blaster is released from ST7 Gallantmon theme deck. This card is what it needs for Security Control to control the lower rookie rank in the board with cheaper cost to play.
And what about Mastemon's decks? Is still good enough? what's new for the deck?
Mastemon is not able to showcase her full potential in BT-05 due to lack of support cards that exist in BT-06 (such as Wizardmon and Mimicmon).
Compared to the JP meta though, EN already has access to the anniversary [P-031] Tailmon so while that would help support Mastemon quite a bit, a purely Mastemon deck will still lack the robustness and aggressiveness of tier-0/1 Lordknightmon (LKM).
In yellow, 1/2 copies of Mastemon can be played in a LKM deck (but some may find Slashangemon more robust). I feel that a pure yellow Mastemon deck may only get as far as Tier-2 or 2.5.
In purple, I think there are better cards to play.