I did a short analysis on our transfer activity since the Wenger era until the present day.
I think this clearly shows that our transfer activity went south after the 2010/11 season, became quite clearly bad after the 2014/15 season and royally fucked us in 2015/16 and 2016/17. (not that we don’t know that).
A lot of these shit investments have already been moved on - Squillaci, Santos, Gervinho, Park, Ox, Podolski, Giroud, Gabriel, Debuchy and Perez. Some still remain - Mustafi, Xhaka, Chambers, Welbeck and Elneny are equal to ~£125m spend on players that need to be re-sold and reinvested in proper players.
Disclaimer* - I’ve used Walcott, Nacho, Sokratis and Arteta as successful purchases loosely. Particularly with Walcott I’ve only listed him as a success because he has always remained a marketable asset, we could always sell him at a big profit (why didn’t we is beyond me) and he still fetched a decent transfer fee in the end.