I believe that A-rating everything is detrimental to a "missions" build. It makes the python too heavy and cripples the jump range. If you're hopping around from system to system doing brief encounters you want to lighten up.
Sure, it reduces your outright staying power in a CZ or REZ but the Python isn't the best ship for a combat-specialised build anyway.
Key things to note about the Python:
- It has hull mass 350T, so "optimal mass" can be surpassed with only class-5 shields. Class-6 shields are more expensive, power-hungry, heavier and rob you of precious internal space for relatively small gains in shield strength.
- The low hull mass means that adding heavy things has a HUGE relative effect on the handling and speeds. You can get away with D-rated thrusters and dirty-drive tuning, or downsized A-rated thrusters. Both will have minimal impact on agility and top speed but offer big improvements in jump range and power requirements.
- If you're not planning on a long-stay hardcore CZ or REZ combat build, you can switch to low-distributor-draw weapons like missiles, cannons and MCs (mod to incendiary if you still want high thermal damage). The lower draw means you can downsize your distributor for reduced mass - and the engineer mods make a HUGE difference to distributors. Literally massive savings here!
- Since the power hungry parts of the build (6A thrusters, 6A shields, 6A sensors, 0A KWS) add relatively little value to missions, you can get away comfortably with a 5A powerplant and low-grade (rank 1 or 2) overcharged mod. Another 30T saved for more jump range.
I have an 80M credit Python build that jumps >34LY and boosts to almost 425m/s. It lets me mine, SRV, passenger, skimmer mission, assassinate etc. For a general "any type of mission" it's superior to both my Trader-specific Anaconda and NH/CZ PVE Corvette, both of which are G5 engineered
specifically for those purposes. For the 160M credit build you've linked, you could actually buy a better "missions-only" Python for 80M and spend the spare 80M credits on an FdL. An 80M credit FdL will be a better combat ship than a 160M credit Python, as someone who has hundreds of hours on both.