Might be an unpopular opinion about Senna. Also some pyke complaining.
I honestly don't mind the fact that she can fill roles other than support. Having a champion that can fill multiple roles is something I do enjoy, but I also understand the negatives of the character potentially being overbearing and taking over other lanes. With Senna, I feel that she's not game breaking if she's not playing support, though I'll admit I've only played two games with her, and both were top lane. If she's top lane, sure she'll outrange and be able to poke, but considering her lack of escapes outside of W'ing and flash, I'd imagine characters that can lock her down will be able to kill her pretty easy, at least until late game where her heal becomes admittedly a little potent. Mid lane it'll depend on match up, though again, a lack of escape means an assassin should have an easy balloon to pop, while mages I'd imagine vary. As for botlane.... well, that's where she's supposed to be.
Riot has already stated they'll nerf her further into support if she's played too often outside of it, which I find is a slight shame. I can understand wanting to avoid the Pyke problem, but I my bronze opinion, Pyke will forever be more troublesome than Senna, even if she isn't nerfed. Which is something I kinda want to talk about as well, as I do have a bias with this post.
Senna is like older marksmen, and suffers from a lot of the problems older marksmen suffer from. Easily bursted due to lack of tank items, relatively immobile, and relies on expensive items to actually kick off(at least in solo lanes). While her support aspects keep her from suffering too badly in the solo lanes, allowing her to sustain and have better trades due to her heal, she also has the high mana costs that keep her from having no downsides. This is why, outside of maybe a few number adjustments, I feel she should be allowed to keep her versatility in role choice. She has weaknesses and downsides that smart players will know how to handle.
Pyke, on the other hand, I despise. Sure he's relegated to mostly support now, but even still I know once he hits 6, chances are he's heading to another lane because he can easily get fed, and feed his teammate at the same time. His assassin weaknesses are made up for by his support abilities, and unlike with Senna, they feel like the make up for them too much. He's got high damage, can pull you, stun you, has a stealth skill(that admittedly has a decently sized warning indicator), and a resetting ranged execute that gives kill gold. Sure he can't gain max health, but it's not like an assassin normally has a ton of health in the first place, and the fact that damage done in a trade with him can easily be healed off by walking out of sight kinda negates that weakness as well. He's just an assassin who's got built in support for himself, and if I see him in a game I know it's never gonna be a fun time. Sure he's got downsides, and I'm sure there are things you can do counter him pretty well, but I'm normally just too tired to care if I see him, even more so when i see the entire team low on health and know a chain execute is about to wipe out most of the squad.
I guess my point is Senna feels fun to play and I'm sure while playing against her may be a mixed bag, I'd rather be able to see and play her in other roles, rather than deal with a Pyke even if he's relegated to support due to how his kit is designed, and the flawed(in my opinion) mix of assassin and support. Senna's strengths and weaknesses from her hybrid class feel a lot more balanced than Pykes, and while the numbers might need tweaking a bit, I feel like it'd be a shame to have her suffer the fate of being nerfed to support only, though I know I'll likely still take her in other lanes anyways. She feels good to take into other lanes, without also feeling like an asshole for doing so.
I'd love to see what others think, how I'm totally wrong, how I'm right, why my opinion doesn't matter as a low elo bronze player, or how this whole post is a mess because I wrote it while nearly passing out and with only 2 games of senna under my belt(one of which involved the saltiest bot lane I've seen in a long time).