I did, too (quite a lot actually). I liked Dash's concept, the speed and the communication by some developpers (like Alexander Block).
What I did not like, was its marketing. Not how they do marketing, but the fact THAT they do marketing. The fact that they have a marketing budget shows that this is a kind of company / startup (with all its advantages and disadvantages).
Bitcoin on the other hand is none of that. Bitcoin is anarchy. Bitcoin is an uncontrolled organism that won't be governed by anybody (or by everybody - which is basically the same thing).

That's why I reduced my Dash holdings (step by step) within the last 2 years to 0.

Concerning your points:

• chainlocks may give DASH theoretical security, whereas BTC offers practical security (partially because of its network effect, its decentrality, the amount of computational work, liquidity)
• The sheer number of coins (1 million or 10 million or 1 billion) doesn't matter. Relevant is the stock-to-flow ratio and the security you have that this scarcity won't be changed. Bitcoin's focus on that scarcity is crystal clear. This is a thing the BTC developpers and/or miners will never change because it's the core selling proposition of BTC (and even if some developpers did change the monetary scheme, immediately there would be a fork and the chain with the better scarcity would win). Because Dash is more centralized (Masternodes, etc.) I can't rely on the hypothesis that Dash won't change its monetary scheme.