A Bing cherry tree growing in southern California will do reasonably well the first several years, just enough to get your hopes up. After that, it will start dwindling away, more & more each year. And will eventually look so sad you'll remove it. If you want a tree that will grow and produce cherries, ask at your nearest independent garden center which cherry will do well where you live. Several will. But only if you obtain the correct kind. Ask when it/they will be available. (In SoCal, bareroot tree fruits are generally available during Jan. & Feb; sometimes in Dec.) As for the flowering cherries and other trees that require substantial amounts of chill -- total hours between 32 and 45 during Dec, Jan & Feb, but subtracting all hours above 65F -- will grow but will bloom erratically & will leaf out erratically. So save yourself a lot of grief and grow "low-chill" fruit tree(s) suited to your region. The large garden centers know which ones they are. But you need to ask. One big problem: Just because a garden center in your region sells a specific fruit tree doesn't mean it will thrive there. Jean, who gardened in Long Beach, CA, for 30-some years.

Cocoplum (note that it's one word, not two) is a small tree and not really a shrub. If you take a walk through a local park, you should see some that are 10, 15, maybe even 20 feet tall. So yes, trim away. HD has a several "dwarf" Crotons - Bush On Fire, Tom Thumb - are two that come to mind, but remember, Crotons are also just small trees looking to grow and get leggy. Consider some ferns as well.

"subgenus" may be more appropriate (or maybe not, taxonomists have put both sweet and sour cherries into the subgenus Cerasus). All these different cherry species are very closely related, if one wants to consider them different species. This is one example where the line separating different species is not a clear one. It could even be possible to consider the different cherry families as subspecies. After all, if they can freely interbreed and hybridize with each other, can they not be considered members within the same species? (by this definition we could divide all cherries into only 2 groups: those with 16 chromosomes and those with 32) Or one could attempt to divide cherries into different families: Sweet cherries (P. avium), sour cherries, Black cherries plus Capulin native to the American continent (put into same group), and Asian flowering cherries. Perhaps better classification could be provided if taxonomists utilized multiple degrees of species relatedness/separation, because it is ambiguous whether some of the different cherries should be classified as entirely separate species or subspecies within a singular species, neither of which would be wholly accurate.

Since the roof downspout is feeding out right at the base of the tree, yes it could certainly be too much water. The planting area appears to be in a bit of a depression as well and that could be compounding the problem. While these trees like even soil moisture, especially during the heat of summer, they absolutely require good drainage. It is very possible the area surrounding the tree is staying too wet too long. You may have the beginning of a root rot going on.