The folk wisdom of "Beware the man with one gun " has analytical backing behind it.
In short, I assigned training cost and skill "profit" to an imaginary rotation of seven different pistols in an Excel profit and loss optimization table. It said pick one and use it ,a lot.
Which makes sense given us humans are limited in resources. Effective training costs time and sometimes money, and spreading both across multiple firearm types is a recipe for confusion and error. Note that the more time and money someone can devote to shooting,the more skill they can build with more firearms-which IMO leads to unrealistic expectations when shooters compare themselves to industry pros and SMEs.
The regular dude with a $100 /2hour monthly shooting + range + time cost budget should ideally pick one pistol and stick with it. Robbie Leatham can shoot ten different models and types because his training resources are exponentially higher in those categories. A pro actually needs to shoot multiple guns at a certain high resource level ; because after running thousands of rounds through Gun X shooting another ten thousand rounds through it doesn't net the same skill benefit the first batch imparted.