So why are these wattages in existence? seems a bit odd when they could have just used 150 or 200, I know this question has likely been asked many times before but if anyone would not mind clarifying again that'd be nice as I don't understand... one of my theories is that maybe it was to compete with incandescent sources of the day... 175W being a bit lower than maybe a 200W Incan lamp but at the same time that logic seems flawed.... help with clarification please?

The original rating was based on replacement of a 400W incandescent by a MA (medium pressure MV) lamp.
The other wattages were based on a compromise between supporting way too much lamp models (when wattages would be to close to each other), against the possibility to optimally design any required installation (when too big differences).
That led to a factor of about 1.4..1.6x between successive wattage levels of the main production, so 400-250-175-125-80-50 wattages.
The probe start MH took over these wattages, because initially they were expected to operate on the same ballasts.
The pulse start lamps, mainly the lower wattages, required a bit more OCV margin, so when designed for the same curents (again, someone initially thought the ballasts could be the same with just added ignitors; it didn't materialize due to secondary effects), it yield lower wattages (150W iso 175W for a 1.5A lamps, or 100W iso 125W for the 1.15A lamps). And this then serves well, when looking for a different than original ballast for the old MV's...