Shouldn't Meggie's Ult counter Lifeline's?

From my experience there is nothing you can really do vs cheaters, not at higher levels - your TTVs, your rank grinders, your pros.

You can take out time to time those soloq hackers that just usually go a bit above masters and just flex like crazy during games pushing everyone and succeeding in doing so even in Master/Pred lobbies. If you 1v2 or 1v3 such players there is a chance that he will probably knock 1 or even 2 of you but if played out well 1v3 is too OP in this game and only rage hacks can maybe pull it off when played well.

Otherwise your typical 3stack "pros" will have one of them run wh - you will notice that most streamers pay 0 attention to the game, rotations, often do not take jump master duties, instead interact with chat and stop doing that only when fight has begun.

All of them will have either softbot or trigger for it. Usually you will see this during the game where you start the fight and it is kinda 50/50 and then suddenly they just beam you/your teammate, get instant knock and push like crazy to finish the job like you were total bots and were not holding your ground a moment ago.
Another more obvious sign - skynade = throwing grande in a way that it explodes not reaching ground / as soon as reaching the ground. And combined with aimbot, those granades fly towards you even when you run away :D basically undogable. Bang bang you are -60 or more health off, if your teammates do not expect that it might hit multiple people for 60+ = easy push because you have basically 1/2 health vs wh, aimbot and perfect coordination of pushes.

Finally when you play Master/Pred lobbies that always contain hackers, you can try and see how perfectly following thing works - create some distance between you and your teammates, say 100m, pretend to be looting, tell teammates not to come towards you. Probably <1 min later a 3 stack or crazy fragger on Ash / Octane will appear and just push in your face, subtle ones use Sparrow and will shoot random arrows exactly where you are to "scan you" before the push. So basically if you don't hold hands in those lobbies you are instadead / one of the first to die in the lobby.

And the list goes on as it is very hard if near impossible to hide hacks, all "best hackers" have done in every game is make people question like 50/50 cases where person is hacking but not bluntly and has skill to make it less obvious, still they e.g. guess right every time the direction enemy cuts corner if there are just two options, start landing 1 mags when it matter the most etc. And there executive decision from moderators must be made -> in case of the Apex it is allowed -> so everyone top level hacks one way or another.

Hope this helps and you will notice hackers more often and report them in game / via web form :) (with hope that it will eventually start working and bans will be issued).