[EPS] is fiddleable by buying back your own shares
I don't think "fiddleable" is quite how I'd describe it! Share buybacks are a legitimate way of adjusting capital to maintain it at the level required. There's also an element of tax planning involved in this too. This kind of capital/treasury management is hardly unique to Ryanair. Also, if you take it to the very extreme, ie buying back all shares, then there is no business: it has been liquidated. I think you'll find in Ryanair's case that retained profits far exceed share buybacks, so that total capital employed has risen substantially over any period you choose to consider. At a guess, I'd suspect that Ryanair has used share buy backs as quasi-dividends.
I do agree, though, that:
Success can be defined many ways
And I'd go further and say that the pre-eminent metrics change due to wider market circumstances. For instance, until the recent stabilisation in the global economy, virtually all airlines were being judged on their rate of "cash burn" and not much else, ie how fast their piles of cash and available credit were depleting in the face of falling passenger numbers/fares. Ryanair went into the crisis with the highest cash balances of any airline in Europe, and they have continued to add to their cash pile even as all the legacy airlines have been burning through theirs and tapping investors via bond issues etc (eg BA, AF/KLM). The LoCos have won the "cash protection" battle quite convincingly over the last 12 months.
I think the other key metric by which to judge virtually any company is its operating margin, basically how much of turnover ends up as profit rather than leaking away as costs. On this measure Ryanair is the leading airline. It means that they can go into any price war confident that they can out last the opposition. It's how they've built their business over the last 20 years, ie simply by having the lowest cost structure in the industry and setting fares accordingly.