M'Bappé is a crack, potentialy Ballon d'Or. Lacazette is "just" very good forward.
Arsenal can't take a crack for the moment, without Champions League. M'Bappé born near Paris, his dad want he play for Paris.
In your current situation, its hard to find better than Lacazette. If Lyon took third place in 2016-2017, he is never come in Arsenal...
Behave!
We're a big club. With or without the CL we can attract top quality. If Lyon won the league unbeaten he'd still join us the season after.