Prior to the release of Madden 17 many players only ran defenses from the Dime formation as they could stop both run and pass; Madden 17 was supposed to see an end to that ability, but, that isn't the case entirely.. I have had great success stopping the run from a Dime defense because essentially there are more avenues for LB's and secondary to attack, because what happens is there is less clogging up of players due to issues with the AI still present in the game.
As for playing with extra safeties: you definitely can go that route, but from my experience, and I am by far no Draft Champions player that is going for the big tournament money, but what matters on defense, and offense for that matter, is still speed.
If you got speed with agility and acceleration 2nd and 3rd, IMO, you can have both an effective defense and offense.. Awareness should be at 85 or above on any player to minimize goofy AI movement...Tackling, even for Safeties, above 70 is solid; and this is going with making a tackle, not worrying about Hit Sticks and forcing fumbles, but pure consistent and solid tackling.
On Defensive line, even running a 3-4 front, where IRL you would want a strong, big player at NT, you don't really need that in Madden; again speed, acceleration and then Finesse Move works to break from blocks and get pressure. No need to worry about having DE's with high strength, Block Shed and tackle, because the AI doesn't work well enough to deal with a rating like tackle very well in close quarters because suction between players is still present. I currently run a 3-4 base with 4-3 DE's and DT; my 2 OLB's are 4-3 LB's with speed and Finesse Move and they actually get more pressure, create a pocket look, better than true 3-4 style LB's because the speed causes the AI players to spread out more which creates more lanes of attack for your other defenders. With this though, you still wanna get Block Shed players above 80...
Now, with those basic ratings covered to get things rolling, you now wanna use the Suggested play section on your play call screen, but you don't want to use the "Suggested plays," you wanna flip to the "Community" play suggestions; those plays are what the game is recording as plays most used by other players for each down and distance, and that is where you are gonna be able to see what works the most often in game, and it works with any playbook you decide to use. It is, IMO, the easiest and quickest way to get an idea of which plays work so you can then start picking from those plays the ones that best fit how you want you defense to look and then try out different line shifts and shades, etc...
Hope this rambling helps some..I am no expect and merely providing insight into how I view and play the game, and do well against the CPU in CFM, Play Now, and MUT..