The short answer is - probably not, but maybe, depending on who it is. But that's impossible to answer right now.
The long answer is - the reason why I'd advise against it is because at your progression, epic champions are often just as valuable, if not moreso, than legendary ones. They're easier to book, and easier to build out for niche roles like Faction Wars, and you'll get more of them.
Usually the guaranteed lego events are not coupled with 2x days, which means you'll have a much greater chance of getting trash rare champs from ancient shards, as opposed to the aforementioned valuable epic champs.
That said - there are certainly some lego champs that would be 100% going for if offered as guaranteed - Ninja's a pretty good example of one. Ditto for someone like Brogni. The last guaranteed legos from ancients were:
Of that set, I would argue the only ones I would have advised pulling for at your progression level would be Kimi and Lix, and possibly Ragash. The rest are all good, yes, but their roles are much too specific to invest so heavily in at your stage.