I'm not really suggesting you play Space Marines over Blood Angels, the DC can still work for you just fine. The rest of your army isn't really addressing the problem you're having. Pretty much nothing aside from your Razorback and maybe your Dreadnought is optimized for dealing with massed infantry. You just aren't shooting enough even within a BA context right now and Tactical squads really aren't the same type of solution as the unit choices I tossed up previously. You need more range and a higher rate of fire. Genestealers can cover almost 24" casually in their move and charge as you're well aware, adding things that have a 24" threat range (more optimally a 12" threat range) is playing into your enemy's strengths. Vehicles can sort of mitigate the risks of being by being higher toughness but even that falls to massed attacks.
I've no experience with Primaris marines to comment there. Every time I look at them I think "but I have BA units that do that sort of stuff already"
EDIT: Do you happen to have another twin assault cannon Razorback? Check out this list, using the models you've mentioned you own.
2x 15 man DC squads - chainswords, jump packs
2x 5 man Tactical squads - heavy bolter, storm bolter
2x 5 man Devastator squads - lascannon (for that signum shot)
Dreadnought - twin autocannon, assault cannon (twin heavy bolter may be better as it lets you put stormbolters on your Razorbacks)
2x Razorbacks - twin assault cannons
Comes out to 1499. Play the Tactical squads close enough for fire support to each other on objectives or put them in the Razorbacks, use the tanks to screen the DC blob, Devastators and Dreadnought hang out way back working together with their 48" weapons to shoot at Flyrants and their shorter ranged weapons to deal with imminent threats.
ALL THE EDITS: Just realized that you could play both the Tactical as Devastator squads for the same cost and get signums on those heavy bolters. It also means Vanguard and Spearhead Detachments, so 5 command points instead of 4 and more accurate heavy weapons for the same points.