Hmm, I'm not sure where to begin with writing out my thoughts in regards to the question. Usually I would give an answer and then explain my thoughts but that would involve having a clear answer in mind. For instance, the big question being whether My Little Pony: Friendship is Magic is as good as it was originally, doesn't have the clearest of answers. I think it's not so much a yes or no answer and more of a change in what the series is like with each season.
For instance, not commenting much on season 3 as it has yet to end, if you were to ask me which of the two completed seasons had the best episodes I would say season 2.
If you were to ask me which of the completed seasons had the worst episodes, I would say season 2.
If you were to ask me which of the completed seasons had the most consistent levels of quality, I would say season 1.
That is how I consider season 1 and 2 to be different. In season 1, nearly all the episodes were of above decent quality, with only one or two episodes not being as good. In season 2, when the episodes were bad, they were really bad, however it balances itself out by when the episodes were good in season 2, they were absolutely fantastic. So in my mind it's more a matter of what you want from the series, a series with consistent level of decent quality or a series with mostly amazing episodes but unfortunately a couple of dreadful ones. I personally think, despite how painful some of the few bad season 2 episodes were for me, that I prefer season 2 over season 1, because the good episodes retain in my memory more, and allow the show to stand out more in my mind.
In regards to season 3, as it has yet to finish I think it's still too early to conclude an opinion on it, but I can say what I think of it so far. I've found season 3 to be rather balanced in quality, like season 1, however that level of quality hasn't been quite as high. It's not bad, but it isn't as great as season 1's balance was. Also I've been at odds with some of their decisions, decisions which have sometimes left negative impacts on otherwise great episodes. In the case of Magic Duel, I found the ending forgiveness of Trixie to be rushed and disappointing, to an otherwise great episode. In the case of Wonderbolt Academy, I found the ending where Spitfire suddenly comes out and says Rainbow was right to interfere with a much more interesting and intriguing future for Rainbow Dash as a character. There's also the Discord episode, which was the first to just mar most of the good the episode itself had going for it. I find the episodes have been well written and funny, but a few of the decisions at the ends of these episodes have been dampening my overall enjoyment.
I'm going to remain positive though. The humour is funny, the characters are well developed, and the world still intrigues me. I don't believe by any account that the overall quality of the series has dropped to the point where it would be worth abandoning it, there has simply been a few bumps natural for most series to have in their lifetime. I do not expect perfection in this series, I expect there will be some episodes that I dislike and some decision in the overall story and character development that I will dislike, but the amount of things I like about this series easily out ways the bad and I'll be sticking with it. So I guess to conclude in regards to the original question; no, this series has not become worse, it has only been suffering from a couple of lapses in quality that is to be expected from any series and has otherwise remained either great or even better than it originally was.
Also I'm way too invested in my fanfiction writing for this series to just drop it.