Abaddon the Rat

If you dual offlane him (Which is probably the most efficient place to put him), you probably lose all tempo control, because that's what offlaners in this day and age do primarly. Now sure, you can instead have a mid-hero that functions in that kind of role; But the problem is that severely limits your list of potential mid-laners, it's basically Lina, Puck, Storm Spirit and Queen of Pain. Maybe the Invoker but he's a rare hero choice nowadays, and anything else is really situational or doesn't fit the position.

Your safe-laner then has to be a really strong core as a result, probably with the capability to flash farm. And you are essentially reliant on this hero for your damage out-put past a certain timing window in the game. Not unheard of, but the problem is in this case you won't have a typical 4 protect 1 set-up which makes that strat a little less viable.

Then you have to consider the fact you are running dual-lanes in this case; Dual lanes mean that your safe-lane is weaker, which when you are a loose form of 4 protect 1 is a horrible thing. You need your safe-lane to have high levels of farm in order for them to be propelled ahead of the enemy core(s). Your dual lanes are also probably a little weaker to rotations than a tri-lane would be, but that's too situational a comment to really be a massive thing against it.

Now, this is just talking about your laning set-up, not how the game develops; The issue with a dedicated rat like Abaddon is that whilst you can't be killed, the pressure your ratting gives is weak in proportion to the potential enemy pressure. Like that is the reason rats are scary, because they push fast enough to threaten or make trades when the enemy pushes, but Abaddon due to his weak tower damage can't do this. Like the only damage your push really does comes from the creep wave, because your right click isn't huge, and mopping up or at least depushing creep waves can be done by a support, especially the ones you see in this meta. And like that doesn't even have to be when at high-ground, because it's not like Abaddon can threaten you if you go up to a creep wave, unlike a Lycan or a Prohet.

So, you don't really have the pressure to force enemy cores back. That's my first issue.

My second issue is that it relies on you having a good laning stage. Aphotic Shield is a great spell for early engagements, but it's still entirely possible that you will get zoned out, because that happens to even the best offlaning cores. And if you get zoned out, or killed, or don't get a good start in the offlane, then you have absolutely no way to catch up. You can't farm stacks and you are a lack-luster ganker. And that basically relegates you to being a support Abaddon with a bit ore farm priority. That's not terrible, but I mean if you aren't doing this rat idea why not have a conventional offlane hero, who can bring more to your team, and definitely act as a tempo controller.

My third issue; The rest of your team is a really bad spot whilst this is happening. Like, they'll primarily be fighting 5v4 (I mean, you can argue the same about Furion, but he can TP into mop up more easily, he can throw his ult to put damage in, and he can tp into other lanes to make ganks happen or assist ganks happen. He's also just plain better at ratting, because he can always cut waves to forstall pushes ect ect. Morphling has Replicate to always put him back in a fight when needed, and Lycan takes builds waaaay too fast to really worry about 5v4's).

Now, 5v4's are not always problematic, because its really dependant on hero composition. But 5v4 when you have only one true damaging core, and a less than ideal tempo controller (I say less than ideal, because you actually see a lot of line-ups with multiple nowadays), and I dare say that in this meta you'll lose a lot over these. Because the enemy offlaner will probably be a better shape, and because fights in this meta generally aren't as reliant on big team-fight combo's, which means that the chances of winning with a numbers dis-advantage is lower.

And frankly if you are bringing a core Abaddon whose build rat items instead of utility or aura's to a fight then again I think it's just a waste of a hero pick, and if you really wanted Abaddon he could've been a support instead. Because you could instead have a Clockwerk or a Centaur Warrunner as your offlaner.

I just don't see it as a strat anywhere other than Pubs, because that's pubs. Everything works in pubs. But primarily because dedicated rats just don't work. Ratting as a result of the way the game transitions is fine, but having a dedicated rat, whose item build is just dedicated for that isn't, from the start isn't. (Note, a natural counter point to this would seemingly be Furion; Furion doesn't build split push. Furion builds push, and happens to have the ability to make that split push seemlessly).

Sorry for the essay, but I just had a lot of fundamental issues with it.