Wait, are you talking permanently or for a single run? If it's permanent, it's WAY overpowered (and can incur in a lot of problems as well), if it's for a single run anything that costs rubies and/or idols is not worth it (remember, unless you are on a very tough objective, the average run will not last more than a few hours).

Besides, how do you propose to combine skills? The new combined crusader gets all of them? It would be extremely unbalanced with skills that multiply damage, even BEFORE the massively overpowered buffs you suggest... not to mention, if you are combining two crusaders into one that means a free slot in the formation, really exploitable. Besides, what model will you use, expecially since with event crusaders the possible combinations are a lot?

Look, I understand that you thought you had a cool idea and wanted to suggest it, but I really feel that suggestions need to be thought through, and this one clearly is not. What you should ask yourself is: would this suggestion improve or reduce the balance of the game? Would it be feasible to implement? What are the possibile complications and exploits? Only after your idea "answers" these questions in a satisfactory manner it can be taken into consideration.

The thing is, you admit being new to the game. Maybe it's better to have some basic understanding of how it works before starting to throw out suggestions, don't you think? It's not even a matter of balance, your suggestion is inherently infeasible (just the fact you didn't consider event crusaders speaks for itself). Ideas that look cool on the surface, and good ideas that can be implemented in the game, are two wildly different things. You need some understanding of the game, and to put some thought into a suggestion, before you can distinguish between the two.