This sounds like a valid concern, but it seems to me, that this is more a problem of balance, i.e. what "x Blocks" means exactly. You could probably make "X" dynamic, maybe by adjusting it every "Y" blocks, but that might open a whole new can of worms
Another problem, as mentioned before, is that it precludes people with 0 XEL from becoming work miners to get XEL. If you want to mine XEL you'd first have to buy XEL, which is less than ideal from the miner's perspective.
Awww, come on, if you spend xxxxx on mining equipment, buying what is probably a two figure $ amount of XEL is not that big of a deal, is it?
I mean, I get what you mean and XEL will miss out on lots of mining power that is pointed elsewhere due to inconvenience, but it would lose even more mining power, if miners would avoid it because of the risk of being outrun. Kind of a "lesser evil" deal.
Additionally, there may be ways to get XEL "outside" of the system,to incentivise new miners to get in. You could create a loan service, where miners can loan a start amount of XEL for BTC or whatever they have laying around.