You can run from almost anything with burn 7 ships. I regularly build fleets around Colossi because they're the biggest thing capable of burn 7 without having to spend dock slots (which I want for other things), and have had no issues running when needed.
Burn 7 is not an issue for the Venture, unless you're obsessing about the highest possible speeds. In which case most cruisers will not be suitable for you either. This is quite an unfair standard to hold against one ship.
CivGrade doesn't increase costs in any way. Unless you're counting the increase from the military conversion, which again is unfair as it's not a requirement.
Their are several major logistical issues with low burn speeds that shouldn't be glossed over as "obsessed with speed".
- Your escape window if a fleet got close via asteroids/debris field/nebula/magnetic field/ect is tiny and nearly every pirate fleet has an equal or higher base burn. This forces more use of emergency burns to escape, wasting more fuel and supplies from CR loss.
- Low burn speed also wastes tons of supplies by costing you days of travel time.
- You can't catch pirates or bounties easily or at all, costing you more supplies, forcing more emergency burns, costing more supplies from CR loss, costing more fuel.
- Missions have timers and you might not be able to get that extra mission done if given the chance, costing you cash.
- Everything takes longer to do, so in addition to not being able to do extra mission in an area because of time restraints you are also spending more time getting every mission done. Costing you cash/supplies.
- Crew costs cash every month, you get less done in the same time frame inflating your costs. 14 burn vs 20 burn is 30% more crew costs to get the same thing done, works the same for supplies.
Everything about 7 burn base is logistically terrible, 8 is acceptable with the +1 burn skill. 9 total burn, meaning 18 travel speed.
12 max speed is... who would even play like this?
14 max speed is terrible
16 max speed is is bad but tolerable
18 max speed is decent
20 max speed is optimal
Venture needs at minimum militarization for 8, plus the skill to be decent (I assume everyone gets the +1 burn speed skill, it's the best QoL skill in the game). I put up with 8 burn only until a get cash or skills to fix it.
It's not about being obsessed with speed, it's not wanting to throw away time/fuel/supplies and cash while pretending nothing is being lost. No mod you can add to your ships is gonna make up for the loss in cash.
Less speed = greater costs/risk & less profit
edit:
"you can run from almost anything with burn 7 ship." And those not included in the "almost anything" cost you at least half your fleet if you are lucky.