Darius' ability to 1v2 while ahead (especially if the reason he's ahead is because he beat his lane opponent, making them behind) is pretty good tbh. It's tough to force him to switch focus when there's only 2 champions and he's got ghost + Cleaver already.
But that's besides the point, to make the top tower weaker wouldn't really provide an incentive to gank. It would only encourage whichever top laner was winning to extend their lead, creating a more snowbally top lane while bot tower is still easier to push down when you have 3-4 champions whaling on it.
From a jungler's point of view, we're talking about an easier 400 gold for the team top lane vs. getting the same 400 gold + helping 2 champions + securing drag by winning down in the bot lane.
What I would do is:
Revert TP changes, or at least reduce the nerf. No real top laner minds being known as the "island" lane, but it'd be nice to have a bridge connecting us to the rest of the game for the first 25 minutes. TP was that bridge, but parts of it were torn away and it requires more time to cross. And even if you do cross, you're often to late.
Change Rift Herald
The thing is tougher than Dragon and does more damage...yet all it does is give you some damage on 1 charged up auto + 5% damage reduction when no allied champions are near.
If you have enough of a lead to take this thing risk-free, it's not even worth it. Herald's strength either has to remain the same and provide new and better stats (for maybe even 2 champions, not just a single-champion buff. This depends on the strength of the buff tbh) or it needs to be much weaker and I'd still advocate a new buff, so long as it represents the strength of herald.
These changes would give Top an avenue to influence the game early again and provides a reasonable buff to be taken top side. With rift herald giving a buff to two champions, and giving top a way to influence the game, you're no longer sacrificing much to come top side.
Rift Herald: relatively strong buff for 2 champions
Drag: relatively weak buff that stacks for 5 champions
Bot side: 3 champions
Top side: 2 champions
perhaps these changes including a weaker top tower in favor of a stronger bot tower would balance out the map's power distribution. I'm still hesitant because with tp changes, I wouldn't want a top laner to be unable to tp bot because his top tower can be taken in a singular push (and with
around, that already happens for just dying in lane once in some cases). So tower switching is still a pretty grey area imo about how it would effect the game.
But hey, we're all theorycrafting here right?